The La1-xCaxMnO3 series of compounds with antiferromagnetic ground states (x 1/2) have been extensively studied due to the novel spin, orbital, and charge-ordering states observed when the calcium concentration is a simple fraction (x = 1/2, 2/3, and 3/4). The ground states of these compositions have been explained by the Goodenough charge, orbital, and spin ordering model. An important issue remaining is the elucidation of how the ground state changes when x is not a simple number. Here we study the magnetic structure of La1-xCaxMnO3 for 0.51 x 0.69 using powder neutron diffraction measurements supported by magnetization data. For compositions with 0.51 x 0.56, the magnetic structure, which we term as an incommensurate charge exchange (CE) structure can be described by two propagation vectors kC = [1/2, 0, 1/2] and kE = [6E, 0, 1/2]. In the second one, the component parallel to the a* axis of the reciprocal lattice changes with the Mn4+ concentration x as 6E approximate to x - 1/2 providing, thus, an unambiguous signature of the adoption of an incommensurate magnetic structure. As x gradually increases, the diffraction data reveal that two magnetic phases-one adopting the incommensurate CE, and one adopting the commensurate "2/3" magnetic structure-co-exist in the concentration regime of 0.57 x 0.61. Around the simple fraction x = 2/3, the magnetic structure can be also described by three propagation vectors, the commensurate kE = [0, 0, 1/2], kC = [1/2, 0, 1/2], and an incommensurate k2/3 = [1/3 + 62/3, 0, 1/2] propagation vector with 62/3 taking negative/zero/positive values for x smaller than/equal to/larger than 2/3, respectively. Our experimental results for 0.51 x 0.56 are neither in favor of a stripe structure consisting of a fine mixture of x = 1/2 and x = 2/3 phases (phase separation) nor of a defect structure in which an appropriate amount of Mn3+-O sheets have been replaced by Mn4+-O sheets (defect structure). A sinusoidal modulated structure has been used as a possible candidate in explaining the experimental neutron diffraction magnetic Bragg peaks. This result may be linked to the presence of a mixed orbital state of the manganese ions.

Doped lanthanum manganite compounds exhibit a range of conducting, electronic and magnetic phases, and, in the case of the Ca-doped series, a phase transition from a ferromagnetic metal to an antiferromagnetic insulator occurs. Here, the authors use ultrahigh-resolution synchrotron X-ray diffraction to track the complex structural behavior of La1-xCaxMnO3 below the charge-ordering temperatures. In the model manganese perovskites La1-xCaxMnO3, several important phenomena have been observed, including ferromagnetic metallic/insulating states, colossal magnetoresistance effects, and charge- and orbital-ordered states. In the past, only compounds with x = 1/2, 2/3 and 3/4 and an insulating ground/antiferromagnetic state have been studied. To fully understand the crystal and electronic structures of these materials, it is important to study compounds with doping levels in the range of 0.5 < x < 2/3. Here we study the crystal structure in a series of compounds with 0.5 < x & LE; 0.6 using ultrahigh-resolution synchrotron X-ray diffraction. The experimental results reveal that all compounds undergo a structural transition at T < T-CO(x) & AP; 200 - 220 K with the concomitant emergence of superlattice Bragg peaks, which can be indexed assuming a superstructure with a modulation propagation vector, & tau;. At the base temperature of 5 K, the modulation vector of the superstructure & tau; = [& tau;(a), 0, 0] is parallel to the a-axis, with & tau;(a) varying linearly with x, as & tau;(a) & AP; 1 - x. Our results may aid attempts to understand more deeply phenomena related to spin, charge, and orbital ordering, as well as colossal magnetoresistance and symmetry breaking and emergent order in quantum states.

During the last decades, the utilization of imaging modalities such as single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI) in every day clinical practice has enabled clinicians to diagnose diseases accurately at early stages. Radiolabeled iron oxide nanoparticles (RIONs) combine their intrinsic magnetic behavior with the extrinsic character of the radionuclide additive, so that they constitute a platform of multifaceted physical properties. Thus, at a practical level, RIONs serve as the physical parent of the so-called dual-modality contrast agents (DMCAs) utilized in SPECT/MRI and PET/MRI applications due to their ability to combine, at real time, the high sensitivity of SPECT or PET together with the high spatial resolution of MRI. This review focuses on the synthesis and in vivo investigation of both biodistribution and imaging efficacy of RIONs as potential SPECT/MRI or PET/MRI DMCAs.

The vortex matter properties of a Ba1-xKxFe2As2 single crystal (T-c = 38.2 K) were studied, by employing both isofield and isothermal ac-susceptibility measurements, chi(n)(f, H-0) = chi(n)' (f, H-0) - i chi(n)'' (f, H-0), in a wide range of frequencies and amplitudes of the applied ac magnetic field. The irreversibility line (H-irr(T, theta)), formally defined by the onset of the third harmonic, is recorded for both H parallel to c-axis and H parallel to ab-plane. It can be reproduced from the empirical equation, H-irr(T) = H-0(1 - T/T-c)(n), with n(c) = n(ab) = 1.24 and mu H-0(0)c = 210 Tesla, torro mu H-0(0)ab = 540 Tesla. The isofield measurements of the first harmonic revealed a narrow diamagnetic peak, related to a local peak of the critical current below the irreversibility line for both H parallel to c-axis and H parallel to ab-plane. The local peak for mu H-0 < 0.2 Tesla is transformed to a sudden drop before it completely disappears. Detailed ac-susceptibility measurements were conducted for frequencies ranging within f = 0.1 10 kHz. From these data, the pinning potential, U, is deduced both as function of temperature and dc magnetic field. These results revealed that the ac response of vortex matter exhibits three distinct dynamic behaviors. By employing a model proposed by Mikitik and Brandt (2001 Phys. Rev. B 64 184514), that is based on a Lindemann type criterion and the collective pinning theory, we reproduced the experimentally recorded vortex matter phase diagram by taking into account both thermal fluctuations and random point disorder. To this effect, we adopted a delta T-c, pinning mechanism, c(L) = 0.25, D-0/c(L) = 1.1-1.5 and a Ginzburg number Gi = 10(-3).

The combination of two imaging modalities in a single agent has received increasing attention during the last few years, since its synergistic action guarantees both accurate and timely diagnosis. For this reason, dual-modality contrast agents (DMCAs), such as radiolabeled iron oxide (namely Fe3O4) nanoparticles, constitute a powerful tool in diagnostic applications. In this respect, here we focus on the synthesis of a potential single photon emission computed tomography/magnetic resonance imaging (SPECT/MRI) DMCA, which consists of Fe3O4 nanoparticles, surface functionalized with 2,3-dicarboxypropane-1,1-diphosphonic acid (DPD) and radiolabeled with Tc-99m, [Tc-99m]Tc-DPD-Fe3O4. The in vitro stability results showed that this DMCA is highly stable after 24 h of incubation in phosphate buffer saline (similar to 92.3% intact), while it is adequately stable after 24 h of incubation with human serum (similar to 67.3% intact). Subsequently, [Tc-99m]Tc-DPD-Fe3O4 DMCA was evaluated in vivo in mice models through standard biodistribution studies, MR imaging and gamma-camera imaging. All techniques provided consistent results, clearly evidencing noticeable liver uptake. Our work documents that [Tc-99m]Tc-DPD-Fe3O4 has all the necessary characteristics to be a potential DMCA.

Radiolabeled magnetic nanoparticles are promising candidates as dual-modality-contrast-agents (DMCA) for diagnostic applications. The immunocompatibility of a new DMCA is a prerequisite for subsequent in vivo applications. Here, a new DMCA, namely Fe3O4 nanoparticles radiolabeled with Ga-68, is subjected to immunocompatibility tests both in vitro and in vivo. The in vitro immunocompatibility of the DMCA relied on incubation with donated human WBCs and PLTs (five healthy individuals). Optical microscopy (OM) and atomic force microscopy (AFM) were employed for the investigation of the morphological characteristics of WBCs and PLTs. A standard hematology analyzer (HA) provided information on complete blood count. The in vivo immunocompatibility of the DMCA was assessed through its biodistribution among the basic organs of the mononuclear phagocyte system in normal and immunodeficient mice (nine in each group). In addition, Magnetic Resonance Imaging (MRI) data were acquired in normal mice (three). The combined OM, AFM and HA in vitro data showed that although the DMCA promoted noticeable activation of WBCs and PLTs, neither degradation nor clustering were observed. The in vivo data showed no difference of the DMCA biodistribution between the normal and immunodeficient mice, while the MRI data prove the efficacy of the particular DMCA when compared to the non-radiolabeled, parent CA. The combined in vitro and in vivo data prove that the particular DMCA is a promising candidate for future in vivo applications.

Dual-modality contrast agents (DMCA), such as radiolabeled magnetic nanoparticles, have attracted significant attention in diagnostic applications due to their potency for the timely and accurate diagnosis of diseases. The hemocompatibility of a candidate DMCA with human blood is essential for the investigation of its application in vivo. In this respect, here we focused on the evaluation of the hemocompatibility of a new DMCA, that is based on iron oxide nanoparticles (i.e. Fe3O4 magnetite), with human red blood cells (RBCs). The specific iron oxide nanoparticles are surface functionalized with 2,3-dicarboxypropane-1,1-diphosphonic acid (-DPD) and radiolabeled with gallium-68 (Ga-68), resulting in Ga-68-DPD-Fe3O4. RBCs of five healthy individuals are incubated at room temperature for 120 min without and with Ga-68-DPD-Fe3O4 at concentrations 0.1 and 1.0 mg/ml. Optical microscopy (OM) and atomic force microscopy (AFM) are employed to assess detailed information on the overall morphological and geometrical characteristics of the entire cell at the microscopic (10(-6) m) level and on the membrane morphology at the nanoscopic (10(-9) m) level. In addition, a standard hematology analyzer (HA) is used to obtain complete blood count information. At the microscopic level, the combined OM, AFM and HA data revealed that the overall shape/size characteristics of RBCs were preserved upon incubation with Ga-68-DPD-Fe3O4 . However, at the nanoscopic level, the AFM results revealed two different kinds of local deconstructions of the RBCs membrane, termed holes and ulcerlike abnormalities, that were observed in both the DMCA-free and DMCA-incubated samples. Holes did not exhibit any statistically significant difference upon incubation with the Ga-68-DPD-Fe3O4 DMCA. On the contrary, ulcer-like abnormalities exhibited two statistically significant differences upon incubation with the Ga-68-DPD-Fe3O4 DMCA. First, increased percentage of RBCs having at least one ulcer-like abnormality; in DMCA-incubated samples 78.6 +/- 11.6% for C-DMCA = 0.1 mg/ml and 80.4 +/- 11.1% for C-DMCA = 1.0 mg/ml, while in DMCA-free samples 61.2 +/- 8.4% prior to and 63.6 +/- 13.5% after incubation. Second, increased number of ulcer-like abnormalities per RBC; in DMCA-incubated samples 4.26 +/- 0.62 for C-DMCA = 0.1 mg/ml and 3.99 +/- 0.97 for C-DMCA = 1.0 mg/ml, while in DMCA-free samples 2.84 +/- 0.54 prior to and 2.98 +/- 0.50 after incubation. The combined OM, AFM and HA results prove fair hemocompatibility of the Ga-68-DPD-Fe3O4 DMCA with human RBCs, thus documenting its potential use in imaging applications.

Magnetoelectric (ME) composites that exhibit both ferroelectric and ferromagnetic properties have attracted significant attention, thanks to their potential applications, e.g., low-energy-consumption storage devices. Here, we study bulk composites based on Pb(Zr0.52Ti0.48)O-3 (PZT) as a piezoelectric (PE) matrix and Fe3O4 nanoparticles (NPs) as soft ferromagnetic (FM) and magnetostrictive additives, in the form PZT-xFe(3)O(4) with 0%<= x <= 50wt.%, all sintered at T=1000 degrees C for 2h in air. We focus our study on a completely insulating sample x=5% and measure its properties at room temperature upon an out-of-plane external electric field, E-ex: namely, piezoelectric response [in-plane strain, S(E-ex)], polarization [P(E-ex)], and relaxation of the remanent magnetization, [m(rem)(t,E-ex)], prepared upon application and removal of an external magnetic field. The peaks observed in the butterflylike S(E-ex) curves at E-peak(+/-)=+/- 6kV/cm and the nucleation field recorded in the P(E-ex) loops at the same range around E-nuc(+/-)=+/- 6kV/cm (both referring to the PZT PE matrix) are clearly imprinted on the relaxation behavior of the m(rem)(t,E-ex) data (referring to the Fe3O4 FM NPs). This experimental fact proves the ME coupling between the PZT matrix and the embedded Fe3O4 NPs. We ascribe this feature to the comparable piezoelectricity of the PZT matrix and the magnetostriction of the Fe3O4 NPs that probably motivate and/or promote a strain transfer mechanism occurring at the PZT matrix-Fe3O4 NP interfaces. Our work proves that the low cost PZT-xFe(3)O(4) composite is a promising candidate ME material for future studies, aiming to potential applications.

Composite magnetoelectric compounds that combine ferroelectricity/piezoelectricity and ferromagnetism/magnetostriction are investigated intensively for room-temperature applications. Here, we studied bulk composites of a magnetostrictive constituent, ferromagnetic Fe3O4 nanoparticles, homogeneously embedded in a ferroelectric/piezoelectric matrix, Pb(Zr0.52Ti0.48) O-3 (PZT). Specifically, we focused on PZT-5%Fe3O4 samples which are strongly insulating and thus sustain a relatively high out-of-plane external electric field, E-ex,E-z. The in-plane strain-electric field curve (S(E-ex,E-z)) was carefully recorded upon successive application and removal of an out-of-plane external magnetic field, H-ex,H-z. The obtained S(E-ex,E-z) data exhibited two main features. First, the respective in-plane piezoelectric coefficients, d(E-ex,E-z) = 200-250 pm/V, show a dramatic decrease, 50-60%, upon application of a relatively low H-ex,H-z = 1 kOe. Second, the process is completely reversible since the initial value of d(E-ex,E-z) is recovered upon removal of H-ex,H-z. Polarization data, P(E-ex,E-z), evidenced that the Fe3O4 nanoparticles introduced static structural disorder that made PZT harder. Taken together, these results prove that the Fe3O4 nanoparticles, except for static structural disorder, introduce reconfigurable magnetic disorder that modifies the in-plane S(E-ex,E-z) curve and the accompanying d(E-ex,E-z) of PZT when an external magnetic field is applied at will. The room-temperature feasibility of these findings renders the PZT-x%Fe3O4 system a solid basis for the development of magnetic-field-controlled PE devices.

The controlled modification of superconductivity by any means is a long-standing issue in low-temperature physics. In this work, we present data on the control of the superconducting properties of conventional low critical-temperature (T-C) Nb thin films with thickness (d(Nb)) =15 and 20 nm under application of reconfigurable strain, S induced by an external electric field, and E-ex to a piezoelectric (PE) single crystal, namely (1 - x)Pb(Mg1/3Nb2/3)O-3 - x PbTiO3 (PMN-PT) with x =0.30-0.31. The experimental results (reduction of T-C and critical current (J(C)) on the order of 6% and 90-100%, respectively) are nicely reproduced with a phenomenological model that incorporates the constitutive relation S(E-ex) that describes the electro-mechanical response of the PE crystal to well-established formulas that describe T-C and J(C) of the SC thin films.

The controlled modification of superconductivity by any means, specifically in hybrid systems, has attracted much interest in the recent decades. Here, we present experimental data and phenomenological modeling on the control of T-C of superconducting (SC) Nb thin films, with thickness 3 nm <= d(Nb) <= 50 nm, under the application of in-plane strain, S(E-ex) induced by an external out-of-plane electric field, E-ex to piezoelectric (PE) single crystals, namely, (1 - x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) (PMN-xPT), with x = 0.27 and 0.31. We report experimental modification of TC of Nb by E-ex, accurately described by a phenomenological model that incorporates the constitutive relation S(E-ex) of PMN-xPT. The systematic experimental-phenomenological modeling approach introduced here is generic and paves the way for an understanding of the underlying physical mechanisms in any SC/PE hybrid. Published by AIP Publishing.

Superparamagnetic iron oxide nanoparticles with well-integrated multimodality imaging properties have generated increasing research interest in the past decade, especially when it comes to the targeted imaging of tumors. Bevacizumab (BCZM) on the other hand is a well-known and widely applied monoclonal antibody recognizing VEGF-A, which is overexpressed in angiogenesis. The aim of this proof-of-concept study was to develop a dual-modality nanoplatform for in vivo targeted single photon computed emission tomography (SPECT) and magnetic resonance imaging (MRI) of tumor vascularization. Iron oxide nanoparticles (IONPs) have been coated with dimercaptosuccinic acid (DMSA), for consequent functionalization with the monoclonal antibody BCZM radiolabeled with Tc-99m, via well-developed surface engineering. The IONPs were characterized based on their size distribution, hydrodynamic diameter and magnetic properties. In vitro cytotoxicity studies showed that our nanoconstruct does not cause toxic effects in normal and cancer cells. Fe3O4-DMSA-SMCC-BCZM-Tc-99m were successfully prepared at high radiochemical purity (> 92%) and their stability in human serum and in PBS were demonstrated. In vitro cell binding studies showed the ability of the Fe3O4-DMSA-SMCC-BCZM-Tc-99m to bind to the VEGF-165 isoform overexpressed on M-165 tumor cells. The ex vivo biodistribution studies in M165 tumor-bearing SCID mice showed high uptake in liver, spleen, kidney and lungs. The Fe3O4-DMSA-SMCC-BCZM-Tc-99m demonstrated quick tumor accumulation starting at 8.9 +/- 1.88% ID/g at 2 h p.i., slightly increasing at 4 h p.i. (16.21 +/- 2.56% ID/g) and then decreasing at 24 h p.i. (6.01 +/- 1.69% ID/g). The tumor-to-blood ratio reached a maximum at 24 h p.i. (similar to 7), which is also the case for the tumor-to- muscle ratio (similar to 18). Initial pilot imaging studies on an experimental gamma-camera and a clinical MR camera prove our hypothesis and demonstrate the potential of Fe3O4-DMSA-SMCC-BCZM-Tc-99m for targeted dual-modality imaging. Our findings indicate that Fe3O4-DMSA-SMCC-BCZM-Tc-99m IONPs could serve as an important diagnostic tool for biomedical imaging as well as a promising candidate for future theranostic applications in cancer.

Electric-field-controlled piezoelectric strain has been used, recently, to modify the superconducting properties in a new class of piezoelectric/superconducting (PE/SC) hybrids. Here, we investigate the appearance of thermomagnetic instabilities (TMIs) and the respective modification of the critical current density (J(C)) through the application of electric field (E-ex) in PE/SC hybrids. Specifically, the SC nanolayers are Nb (thickness, d(SC) = 20 nm) deposited on both surfaces of PE macroscopic crystals of (1-x)Pb(Mg-1/3 Nb-2/3)O-3-xPbTiO(3) (PMN-PT) with optimum composition x = 0.31 (thickness, d(PE) = 0.5-0.8 mm). The appearance of TMIs and the modification of J(C) by E-ex is studied for two PMN-PT crystals of drastically different surface roughness (Sa). In the case of the PMN-PT crystal with low Sa (on the order of a few tenths of nm) TMIs are absent so that J(C) does not change under the variation of E-ex. On the contrary, in the case of the PMN-PT crystal with high Sa (on the order of a few hundreds of nm) E-ex induces TMIs in the Nb nanolayers. Specifically, the number of TMIs exhibits a non-monotonic increase on E-ex, thus causing a non-monotonic degradation of J(C). These experimental data are interpreted in terms of the variation of both volume strain and surface roughness on E-ex. This work highlights practical means to control the current-carrying capability of SC nanolayers through strain provided by PE substrates. (C) 2017 Elsevier B.V. All rights reserved.

The aim of this study was to develop a dual-modality PET/MR imaging probe by radiolabeling iron oxide magnetic nanoparticles (IONPs), surface functionalized with water soluble stabilizer 2,3-dicarboxypropane-1,1-diphosphonic acid (DPD), with the positron emitter Gallium-68. Magnetite nanoparticles (Fe3O4 MNPs) were synthesized via coprecipitation method and were stabilized with DPD. The Fe3O4-DPD MNPs were characterized based on their structure, morphology, size, surface charge, and magnetic properties. In vitro cytotoxicity studies showed reduced toxicity in normal cells, compared to cancer cells. Fe3O4-DPD MNPs were successfully labeled with Gallium-68 at high radiochemical purity (> 91%) and their stability in human serum and in PBS was demonstrated, along with their further characterization on size and magnetic properties. The ex vivo biodistribution studies in normal Swiss mice showed high uptake in the liver followed by spleen. The acquired PET images were in accordance with the ex vivo biodistribution results. Our findings indicate that 68 Ga-Fe3O4-DPD MNPs could serve as an important diagnostic tool for biomedical imaging.

The competitive nature of ferromagnetism and superconductivity in Ferromagnet/Superconductor (FM/SC) hybrids has attracted much interest in the last decades. In particular, the superconducting magnetoresistance (SMR) observed in FM/SC/FM trilayers (TLs) is related to the manipulation of the transport properties of the SC interlayer by the magnetic domain structure of the FM outer layers with out-of-plane anisotropy. In our recent work [Sci. Rep. 5, 13420 (2015)], a phenomenological model was proposed that describes successfully the scaling of the SMR magnitude with the relevant macroscopic parameters and microscopic length scales of the SC and FM structural units. Based on this model, here we investigate the contribution of the parameters that affect indirectly the SMR magnitude and do not appear in the original model. To this end, the parameters of both the SC interlayer (i.e., the thickness, dSC, the mean free path, l, the coherence length, xi(0), etc.) and the FM outer layers (i.e., the thickness, d(FM)) are examined. The theoretical simulations presented here and experimental data unveil the indirect contribution of these parameters on the magnitude of the SMR and confirm the predictive power of the original phenomenological model. Accordingly, this model can be employed as a generic formula to combine successfully all involved parameters in every kind of FM/SC/FM TLs, ultimately optimizing the magnitude of the SMR. (C) 2016 AIP Publishing LLC.

The ferroelectric compound family Pb(ZrxTi1-x,)O-3 (PZT) is one of the most investigated and widely used piezoelectric materials. Optimization of the piezoelectric coefficients is observed for x similar to 0.52 (Pb(Zr0.52Ti0.48)O-3) and is further promoted by the increase of grain size (OS). However, in some cases the piezoelectric properties of Pb(Zr0.52Ti0.48)O-3 deteriorate upon processing due to the decrease of density, p, that is mostly ascribed to the appearance of byproduct phases. In the present study we discuss the influence of the processing conditions on the piezoelectric properties for polycrystalline Pb(Zr0.52Ti0.48)O-3, specifically focusing on the sintering temperature, 1100 degrees C Tsin <= 1250 degrees C. To this end, we use atomic force microscopy (AFM), Archimedes' method, x-ray diffraction (XRD) and a newly introduced local technique, based on a conventional optical microscope, which is further developed here to accommodate non-clamped specimens. The data obtained via this technique in the regime of relatively high electric fields evidence that the absolute piezoelectric coefficients, 141(i = x, y) show a non -monotonic behavior with an unexpectedly high maximum value broken vertical bar d broken vertical bar similar to 1100 pm V 1 at 7 = 1180 degrees C. These features are accompanied by a progressive increase of coercivity, reaching maximum value Ecj 4.5-5.0 kV cm I (i = x, y) at Tsin = 1250 degrees C. 'lb explain these findings, the Idzil coefficients are compared with the microstructure and compositional information, coming from AFM, Archimedes' method and XRD data. We conclude that the significantly high 141 values observed for samples prepared at Tsin = 1180 degrees C are motivated by the increase of mean GS, < GS >, while for Tsin > 1180 degrees C the decrease of density, p, ascribed to the appearance of byproduct phases, dominates and deteriorates Id2 I. These experimental results on broken vertical bar d broken vertical bar(T-sin) are reliably reproduced by a phenomenological model with reasonable assumptions for < GS > (7) 1 and rho(T(si)n). The unexpectedly high piezoelectric coefficients, broken vertical bar d(zi)broken vertical bar similar to 1100 pm V-1, reported here for the first time, are provocative and call for utilization of the introduced approach in the investigation of the respective properties of other compounds.

Magnetoresistance effects observed in superconductor/ferromagnet (SC/FM) hybrids, SC/FM bilayers and FM/SC/FM trilayers, have attracted much interest in recent years. Here we focus on the stray-fields-based superconducting magnetoresistance effect (sMRE) observed in Co(d(Co))/Nb(d(Nb))/Co(d(Co)) trilayers with sufficiently thick Co outer layers so that out-of-plane magnetic domains (MDs) and MDs walls (MDWs) emerge all over their surface when subjected to a parallel external magnetic field, H-ex equal to the coercive field, H-c. Asking for the optimum conditions to maximize the sMRE, we explore the interference between three basic length scales of the SC and FM structural units: the thickness of the SC interlayer (d(SC)), the zero-temperature coherence length (xi(0)) and the width of out-of-plane MDs (D-MDs). To this effect, simulations-based modeling of the transverse stray dipolar fields, H-z,H-dip that emerge at the interior of the out-of-plane MDs is performed. Both cases of homogeneous and inhomogeneous micromagnetic characteristics (saturation magnetization, M-sat and width, DMDs) of the out-of-plane MDs are investigated. Furthermore, the influence of the microstructure of the bottom and top Co layers on the macroscopic coercive field of the TLs is addressed. The obtained modeling results respond well when tested against experimental data. The generic criteria reported here on the optimum matching of d(SC), xi(0) and D-MDs aiming to maximize the sMRE magnitude in relevant FM/SC/FM trilayers, can assist the design of relevant cryogenic devices. (C) 2016 Elsevier B.V. All rights reserved.

Nanogels based on biocompatible, dual pH- and temperature-sensitive poly(2-(diethylamino)ethyl) methacrylate (PDEAEMA) have been successfully used as nanocontainers for the encapsulation of magnetite, Fe3O4 magnetic nanoparticles (MNPs). For this purpose, citric acid-coated MNPs were encapsulated into previously synthesized PDEAEMA-based nanogels using a poly(ethyleneglycol)-based stabilizer. After the encapsulation of the magnetite MNPs, the so-called magneto-nanogels (MNGs) were proved to be multiresponsive on temperature, pH, and magnetic field and colloidally stable. Moreover, preliminary studies on the biocompatibility of these MNGs with cells of human peripheral blood were performed and evidenced quite tolerable biocompatibility, thus suggesting potential use in biomedical applications. (C) 2015 Wiley Periodicals, Inc.

In the last decades, many superconductor-based devices have been utilized in practical applications that refer to the production/sensing of ultra-high/low magnetic fields, resistive storage of data, etc. The superconducting magnetoresistance effect (sMRE) observed in ferromagnetic/superconducting/ferromagnetic trilayers (TLs) has been widely studied in the literature. Here, we investigate Ni80Fe20/Nb/Ni80Fe20 and Co/Nb/Co TLs on a comparative basis and we provide technical guidelines that empower us to design magnetic field sensors and magnetic field-controlled supercurrent switches for cryogenic applications. The performance of these TLs has been studied in great detail. It turned out that Ni80Fe20-based TLs are applicable in the regime of low magnetic fields (on the order of a few hundred Oe) due to their magnetically soft character, while Co-based ones are effective at relatively higher magnetic fields (on the order of a few thousand Oe) owing to their magnetically harder behavior. The Ni80Fe20-based TLs exhibit a sMRE magnitude, (R-max - R-min)/R-nor x 100 %, on the order of 30-50 % and a field sensitivity, dR(H)/dH, on the order of 4.0-6.0 mOhm/Oe. The Co-based TLs have higher sMRE magnitude on the order of 30-100 %; however, they exhibit lower field sensitivity on the order of 0.3-0.6 mOhm/Oe. Finally, the Co-based TLs exhibit an abnormal behavior of the upper critical field line, H-c2(T), at low magnetic fields. This feature is absent in the Ni80Fe20-based TLs. Due to the differences outlined above, the Ni80Fe20-based and Co-based TLs can be possibly utilized in two distinct categories of devices, namely magnetic field sensors and magnetic field-controlled supercurrent switches, respectively.

Magnetoresistance effects observed in ferromagnet/superconductor (FM/SC) hybrids, FM/SC bilayers (BLs) and FM/SC/FM trilayers (TLs), have attracted much interest. Here, we focus on the stray-fields-based superconducting magnetoresistance effect (sMRE) observed in Co(d(Co))/Nb(d(Nb))/Co(d(Co)) TLs with sufficiently thick Co outer layers so that out-of-plane magnetic domains (MDs) and MDs walls (MDWs) emerge all over their surface when subjected to a parallel external magnetic field, H-ex, equal to the coercive field, H-c. To explore the conditions necessary for maximization of the sMRE, we focus on the different kinds of the stray dipolar fields, H-dip, that emerge at the interior of the out-of-plane MDs and at the boundaries of MDWs; these have a different inherent tendency to create straight and semi-loop vortices, respectively. In the recent literature, the creation of straight and semi-loop vortices has been addressed at some extent both theoretically [Laiho et al., Phys. Rev. B 67, 144522 (2003)] and experimentally [Bobba et al., Phys. Rev. B 89, 214502 (2014)] for the case of FM/SC BLs. Here, we address these issues in FM/SC/FM TLs in connection to the sMRE. Specifically, we focus on an experimental finding reported recently [D. Stamopoulos and E. Aristomenopoulou, J. Appl. Phys. 116, 233908 (2014)]; strong magnetostatic coupling of the FM outer layers is accompanied by an intense sMRE in TLs in which the thickness of the SC interlayer, d(SC), matches the width of MDWs, D-MDWs. To investigate this finding, we employ simulations-modeling and energy-considerations and propose two quantitative criteria that facilitate the creation of straight vortices over semi-loop ones. The first focuses on the maximization of the stray H-dip that occur at the interior of the out-of-plane MDs. The second enables the estimation of a crossover between the preferable creation of one kind of vortices over the other. Both criteria respond well, when tested against experimental results. These generic criteria on the interference between d(SC) and D-MDWs can assist the design of cryogenic devices based on FM/SC/FM TLs. (C) 2015 AIP Publishing LLC.

Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent 'on' and 'off', thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.

In recent years the microstructure, mechanical and magnetic properties of Eurofer-97 steel are studied intensively due to its application in nuclear fusion power plants. Its microstructure is usually accessed by means of electron microscopy. Here we present an alternative approach utilizing Atomic Force Microscopy (AFM) to study as-received Eurofer-97 steel. We recorded both the Height Signal (HS) and Phase Signal (PS) that provided information on the morphologic and inelastic topography, respectively. With the HS we detected spherical particles (SPs) of size 50-2000 nm. Interestingly, micrometer SPs (0.1-2.0 mu m) are randomly distributed, while nanometer SPs (50-100 nm) are sometimes arranged in correlation to grain boundaries. The PS clearly revealed that the micrometer SPs exhibit inelastic properties. Though we cannot identify the elemental composition of the SPs with AFM, based on relevant electron microscopy data we ascribe the nanometer ones to the TaC, TiN and VN and the coarse micrometer ones to M23C6 (M=Cr, Fe). The latter class of SPs can probably be active sites that influence the mechanical properties of Eurofer-97 steel upon annealing as observed in relevant electron microscopy based studies.

Low-dimensional hybrid structures of heterogeneous constituents usually exhibit abnormal properties, a fact that makes such hybrids attractive for various cryogenic and room-temperature applications. Here, we studied Co/(1 - x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3)/Co (Co/PMN-xPT/Co) with x = 0.29 and 0.30, specifically focusing on the evolution of the remanent ferromagnetic state, m(rem) of the Co outer layers in the whole temperature range from 300K down to 10 K, upon application of an external electric field, E-ex. We observed that m(rem) was vulnerable to degradation through the occurrence of electric field-induced magnetic instabilities (EMIs) that appeared only when E-ex not equal 0 kV/cm and were facilitated as E-ex increases. However, EMIs completely ceased below a characteristic temperature T-ces = 170 K even for the maximum vertical bar E-ex vertical bar = 5 kV/cm applied in this work. A direct comparison of the magnetization data of the Co/PMN-xPT/Co hybrids reported here with the electromechanical properties of the parent PMN-xPT crystals plausibly indicates that EMIs are motivated by the coupling of the ferromagnetic domains of the Co outer layers with the ferroelectric domains of the PMN-xPT crystal. These results highlight the drawback of EMIs in relevant hybrids and delimit the temperature regime for the reliable operation of the Co/PMN-xPT/Co ones studied here. (c) 2014 AIP Publishing LLC.

The Exchange Bias (EB) effect is observed at the interface of Antiferromagnet/Ferromagnet (AF/FM) structures and depends on the interface roughness (IR). Until today, only low IR values, usually below 10 nm, have been investigated. Here we investigate an extended range of IR through controlling the surface roughness (SR) of the employed substrates. We employ CoO/Co bilayers (thickness within 10-60 nm), a classic AF/FM structure that exhibits intense EB. ZnO was employed as the substrate in both film and bulk forms, enabling us to vary the SR up to 840 nm. Our data reveal a strong relative decrease, ranging within 20-65%, of both the shift H-shift(EB) and coercive H-c(EB) fields upon increase of SR (IR), for both parallel and normal magnetic field-sample configurations. For the explanation of these findings we propose that in thin AF/FM structures deposited on rough substrates the local magnetization, M-f of the FM is 'locked' mainly in-layer due to shape anisotropy, thus it is forced to follow the morphologically rough landscape of the substrate. This imposes misalignment between M-f, that is 'directionally random', and H-ex, that is 'directionally oriented'. This weakens the biasing potential of H-ex on M-f and reduces the relative macroscopic parameters H-shift(EB) and HcEB

Using a vector network analyzer equipped with a calibrated rectangular wave guide the electric permittivity and the element of the magnetic permeability tensor for Y3Fe5O12, ZnFe2O4 and NiFe2O4 are measured. The electric permittivity can be estimated from the body resonances (d = n lambda/2) if a sufficient long sample is used. The estimation of the magnetic permeability tensors' parameters can be estimated comparing the experimental results with computer simulations using the magnetic properties of the materials as derived from the magnetic measurements.

The properties of multiferroic and specifically piezoelectric (PE) materials are, nowadays, intensively investigated by means of well established, however relatively complicate methods. In this work we present a method for the direct visual demonstration of the underlying electro-mechanical processes occurring in PE materials and the estimation of the respective coefficients d(ij). The method is based on the utilization of optical microscopy for the local observation of the deformation of a PE specimen upon application of an electric field. The direct comparison of the snapshots obtained before and after application of the electric field and simple algebraic calculations enables the estimation of the d(ij) coefficients. The method was evaluated in unpoled single crystals of 0.71Pb(Mg1/3Nb2/3)O-3-0.29PbTiO(3), at room temperature. Various locations of each crystal surface were surveyed. Non-homogeneous electro-mechanical response was observed. Accordingly, the estimated d(ij) coefficients depended on the specific location of the crystal surface. Specifically, the d(zx) coefficient ranged within 500-1000 pm/V over the investigated locations (for electric fields E<1kV/mm). The present method directly unveils non-homogeneous electro-mechanical processes occurring at the surface of PE crystals and clarifies how these observations can be quantified through the respective d(ij) coefficients.

Artificial (CoO-)Co/Nb/Co trilayers (TLs) are studied by means of magnetization, transport, and magnetic force microscopy measurements. By using these TLs as a model system, we provide definite means to distinguish the exchange-fields and stray-fields based magnetoresistance effects observed in relevant Ferromagnetic/Superconducting/Ferromagnetic (FM/SC/FM) structures. Accordingly, we isolate and exclusively focus on the stray-fields version, to report a complete supercurrent switch, Delta R/R-nor approximate to 100%, achieved at operating temperature T > 4.2 K. Detailed series of Co(60 nm)/Nb(d(Nb))/Co(60 nm) TLs are studied, in which all crucial parameters that relate to the outer Co layers and to the Nb interlayer were systematically varied to unveil the factors that motivate and/or promote the observed effect. We propose a compact model that fairly captures the underlying physics of the Co(60 nm)/Nb(d(Nb))/Co(60 nm) TLs studied here and can be generalized to assist understanding of the relevant processes in every kind of FM/SC/FM TLs. The presented results and accompanying model are both provocative for basic research and attractive for the design of cryogenic devices. (C) 2014 AIP Publishing LLC.

Nowadays, Ferromagnetic/Superconducting/Ferromagnetic trilayers (FM/SC/FM TLs) are intensively studied. Here, based on (CoO-) Co/Nb/Co TLs of thin Nb interlayer (below 30 nm) we introduce two classes of low-T-c SC-based cryogenic devices, depending on the thickness of the Co outer layers and the presence of a CoO underlayer. An extended range of Co thickness (from 10 to 80 nm) was investigated and an underlayer of CoO was selectively employed, practically aiming to control in-plane and out-of-plane magnetization processes through utilization of shape anisotropy and exchange bias. To this effect magnetic force microscopy, magnetization and magnetoresistance data are presented. Ancillary atomic force microscopy and Rutherford back scattering data are presented, as well. CoO-Co/Nb/Co TLs of the first class have thin Co outer layers (10-30 nm) and are further assisted by the presence of a CoO underlayer to behave as efficient spin valves (Delta R/R-nor = 1.5% and Delta R/R-min = 2.4%) under the action of the FMs in-plane exchange fields; the effect is termed superconducting Spin-Valve Effect (sSVE). Co/Nb/Co TLs of the second class have thick Co outer layers (50-80 nm) and without the need of a CoO underlayer act as almost absolute supercurrent switches (Delta R/R-nor = 97.7% and Delta R/R-min = 28000%) under the action of FMs out-of-plane stray fields; the effect is termed superconducting Magneto-Resistance Effect (sMRE). The properties of these (CoO-) Co/Nb/Co TLs resemble the behavior of standard FM/normal-metal/FM and FM/insulator/FM TLs that exhibit the effects giant (GMR) and tunnel (TMR) magnetoresistance, respectively. Aiming to utilize the FM/SC/FM TLs studied here into cryogenic applications we thoroughly surveyed their operational H-T phase diagram and discuss how can be used to realize binary ('0'-'1') elemental devices for information management in both read heads and memory units. The underlying physical mechanisms responsible for the sSVE and sMRE observed in the two different classes of TLs, that is CoO-Co/Nb/Co and Co/Nb/Co, respectively and the technical requisites that the SC and FM ingredients should meet are discussed.

Ferroelectric materials have attracted much interest due to their wide and important technological applications. Regarding their piezoelectric properties, these materials are evaluated by means of relatively complicate global methods. In this work a comparatively simple and efficient local method for the direct estimation of the d(ij) coefficients is presented. The method is based on conventional optical microscopy (OM) and advanced Atomic Force Microscopy (AFM) employed to image the local deformation of a specimen upon variation of a dc electric field. The feasibility and reliability of the method is demonstrated at room temperature in single crystals of (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3). Non-homogeneous electromechanical processes are detected. Accordingly, the estimated d(ij) coefficients exhibit a spatial variation over the crystal surface. Except for electro-mechanical systems, the introduced local method could find wide application for the investigation of spatially non-homogeneous properties that possibly exist in relevant magneto-mechanical and thermo-mechanical complex systems. (C) 2014 Elsevier B.V. All rights reserved.

In ferromagnetic/superconducting (FM/SC) planar hybrids, a reentrance of the upper-critical field line H-c2(T) is observed close to T-c. The effect is generally ascribed to the so-called domain-wall superconductivity and has been theoretically explored in great detail. Experimental investigations are limited mostly to FM/SC bilayers in which the FM layers host out-of-plane magnetic domains of strong anisotropy and large width (>300 nm), the SC layer is quite thick (>30 nm), and the external magnetic field was applied normal. To expand our knowledge to until now unexplored conditions, we study a series of Co(d(Co))/Nb(d(Nb))/Co(d(Co)) trilayers under a parallel magnetic field; Co outer layers exhibit out-of-plane magnetic domains of weak anisotropy and small width (<150 nm) and the Nb interlayer is very thin (<20 nm). We demonstrate a strong reentrance of H-c2(T) that can be tuned through the irreversible magnetization processes of the FM outer layers, the two-dimensional character of the SC interlayer, and the matching between the interfering SC and FM length scales. These results refine the nature of the reentrance of H-c2(T) in FM/SC hybrids and can motivate new theoretical and experimental investigations. (C) 2014 AIP Publishing LLC.

Reduced-activation ferritic-martensitic steels are promising candidates for structural applications in future nuclear fusion power plants. Oxide dispersion strengthened ODS-Eurofer and Eurofer 97 steels were cold rolled to 80% reduction in thickness and annealed in vacuum for 1 h from 200 to 1350 degrees C to evaluate both their thermal stability and magnetic behavior. The microstructural changes were followed by magnetic measurements, in particular the corresponding variation of the coercive field (H-c), as a function of both annealing and tempering treatments. Results show that Y2O3 nanoparticles strongly affect the mechanical properties of ODS-Eurofer steel but leave their magnetic properties fairly unchanged when compared with Eurofer-97 steel. (C) 2012 Elsevier BM. All rights reserved.

Background: In hemodialysis (HD) patients, anemia relates to three main factors: insufficient production of erythropoietin; impaired management of iron; and decreased lifespan of red blood cells (RBCs). The third factor can relate to structural deterioration of RBCs due to extrinsic (extracorporeal circuit; biochemical activation and/or mechanical stress during dialysis) and intrinsic (uremic milieu; biochemical interference of the RBC membrane constituents with toxins) mechanisms. Herein, we evaluate information accessed with advanced imaging techniques at the cellular level. Methods: Atomic force and scanning electron microscopes were employed to survey intact RBCs (iRBCs) of seven HD patients in comparison to seven healthy donors. The extrinsic factor was investigated by contrasting pre- and post-HD samples. The intrinsic environment was investigated by comparing the microscopy data with the clinical ones. Results: The iRBC membranes of the enrolled HD patients were overpopulated with orifice-like (high incidence; typical size within 100-1,000 nm) and crevice-like (low incidence; typical size within 500-4,000 nm) defects that exhibited a statistically significant (P < 0.05) relative increase (+55% and +350%, respectively) in respect to healthy donors. The relative variation of the orifice and crevice indices (mean population of orifices and crevices per top membrane surface) between pre- and post-HD was not statistically significant (-3.3% and +4.5%, respectively). The orifice index correlates with the concentrations of urea, calcium, and phosphorus, but not, however, with that of creatinine. Conclusion: Extracorporeal circulation is not detrimental to the structural integrity of RBC membranes. Uremic milieu is a candidate cause of RBC membrane deterioration, which possibly worsens anemia.

In this paper, we present a patch antenna design and fabrication that uses a ferrimagnetic compound, Yttrium Iron Garnet (YIG), as part of its substrate. It is proved via both numerical simulations and experimental measurements, that with suitable application of an external magnetic field, a reconfigurable behavior in terms of the polarization characteristics can be achieved. The antenna is reconfigured from a single band linear polarized to a dual band circular polarized one, with different polarization sense in each resonance band. Mixtures containing YIG and epoxy resin in various consistencies have been examined.

Zinc ferrites, ZnFe2O4 and zinc ferrite nanoparticles substituted with indium and yttrium, Zn1-xInxFe2O4 and ZnYxFe2-xO4 (0 <= x <= 0.3), were synthesized by co-precipitation method. We have investigated the effect of composition on the cation distribution in the spinel structure, and on the magnetic properties with a view to obtain magnetic ceramics with improved properties compared to their bulk counter parts. The results of X ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the nanoscale dimensions and spinel structure of the samples. The estimated crystallite size lies within the range 4-10 nm. Additional experiments had been conducted using a scanning mobility particle sizer spectrometer (SMPS) in order to measure the number size distribution of the nanoparticles. Mossbauer spectroscopy was used to investigate the cation distribution between the tetrahedral and octahedral sites and the formation of the partially inverse spinel. The study of the magnetic properties showed that the hysteresis loops do not saturate even in the presence of high magnetic fields, confirming the superparamagnetic single domain nature of the samples. The particle size and composition variations (e.g. addition of yttrium and indium) cause significant structural rearrangements which affect the magnetic behavior of these materials. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The superconducting magnetoresistance effect (SMRE) observed in trilayers (TLs) consisting of a superconducting (SC) Nb interlayer and two outer ferromagnetic (FM) Ni80Fe20 and Co layers is studied. We observed that the SMRE exhibits a pronounced magnitude (R-max - R-min)/R-nor of order 45 % and 86 % for the NiFe-based and Co-based TLs, respectively. For the NiFe-based TLs, the dynamic transport behavior of the observed SMRE is presented through detailed I-V characteristics that exhibit a nonlinear character even extremely close to the critical temperature, T-c(SC). Also, the detailed evolution of the longitudinal and transverse components of the TL magnetization from close to well below T-c(SC) is presented. For the Co-based TLs, the obtained magnetization and transport data justify that a strict requisite for the observation of a pronounced SMRE across T-c(SC) is that the coercivities of the FM layers should be similar. The combined data on the NiFe-based and Co-based TLs show that across the superconducting transition the SMRE is influenced by out-of-plane stray-fields, attaining pronounced values when the respective coercive fields coincide, thus enabling the transverse magnetic coupling of the outer FM layers through the SC interlayer.

In many cases, technological advances are based on artificial low-dimensional structures of heterogeneous constituents, thus called hybrids, that when come together they provide stand-alone entities that exhibit entirely different properties. Such hybrids are nowadays intensively studied since they are attractive for both basic research and oncoming practical applications. Here, we studied hybrids constituted of piezoelectric (PE) and ferromagnetic (FM) components in the form FM/PE/FM, ultimately aiming to provide means for the controlled modulation of the properties of the FM electrodes, originating from the strain imposed to them by the PE mediator when an electric field is applied. The PE component is in single crystal form, 0.71Pb(Mg1/3Nb2/3)O-3-0.29PbTiO(3) (PMN-PT), while the FM outer layers are Cobalt (Co) in thin film form. Detailed magnetization measurements performed under variation of the electric field applied to PMN-PT demonstrated the efficient modulation of the properties of the Co electrodes at low temperature (coercive field modulation up to 27% and saturation magnetization absolute modulation up to 4% at T = 10K for electric field not exceeding 6 kV/cm). The modulation degree faints upon increase of the temperature, evidencing that the thermal energy eventually dominates all other relevant energy scales. Candidate mechanisms are discussed for the explanation of these experimental observations. The results presented here demonstrate that commercially available materials can result in quantitatively noticeable effects. Thus, such elemental Co/PMN-PT/Co units can be used as a solid basis for the development of devices. (C) 2013 AIP Publishing LLC.

Together with impaired production of erythropoietin and iron deficiency, the decreased lifespan of red blood cells (RBCs) is a main factor contributing to the chronic anaemia observed in haemodialysis (HD) patients. Atomic force microscopy is employed in this work to thoroughly survey the membrane of intact RBCs (iRBCs) of HD patients in comparison to those of healthy donors, aiming to obtain direct information on the structural status of RBCs that can be related to their decreased lifespan. We observed that the iRBC membrane of the HD patients is overpopulated with extended circular defects, termed 'orifices', that have typical dimension ranging between 0.2 and 1.0 mu m. The 'orifice' index-that is, the mean population of 'orifices' per top membrane surface-exhibits a pronounced relative increase of order 54 +/- 12% for the HD patients as compared to healthy donors. Interestingly, for the HD patients, the 'orifice' index, which relates to the structural status of the RBC membrane, correlates strongly with urea concentration, which is a basic index of the uraemic milieu. Thus, these results indicate that the uraemic milieu downgrades the structural status of the RBC membrane, possibly triggering biochemical processes that result in their premature elimination from the circulation. This process could decrease the lifespan of RBCs, as observed in HD patients.

In this study the authors introduce the utilisation of ferrimagnetic compounds into an antenna design and investigate the capability of controlling the antenna properties by means of an external magnetic field. After intensive study of the material properties, the ferrimagnetic compound yttrium iron garnet (YIG) was found to be the best candidate for the proposed novel antenna design. The authors provide a patch antenna design with a part of the dielectric substrate replaced by YIG compound. They have investigated the influence of this compound on the antenna's polarisation properties under the application of an external magnetic field. The authors clearly demonstrate that the type and the sense of the antenna polarisation are strongly influenced by the YIG substrate, because they change with respect to the direction and the magnitude of the external magnetic field. Moreover, the authors have proved that the presence of this material induces non-reciprocal properties in the antenna's operation, changing the antenna properties with respect to receiving or transmitting mode.

High-resolution electron backscatter diffraction (EBSD) technique and DC magnetization were used to characterize a Cu-Nb reinforced bronze route Nb3Sn superconducting multifilamentary wire. The results of DC-magnetization show an extended regime of magnetic reversibility in the operational magnetic field-temperature phase diagram. This observation is discussed in terms of microstructure characteristics of the A15 phase such as grain size, grain boundary misorientation angle distribution, tin gradient across the filaments and residual strain, in connection to the literature. (C) 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.

We have studied the phase diagram of a Ba-1 xKxFe2As2 (T-c = 36.9 K) single crystal superconductor by employing ac-susceptibility measurements, both as a function of temperature for constant external magnetic field and of magnetic dc-field for constant temperature for angles Theta = (sic)(H, c-axis) = 0 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees and 90 degrees, between the c-axis and the magnetic field. The irreversibility lines (H-irr(T, H)) are estimated from the onset of non-zero values of the amplitude of the third harmonic susceptibility. H-irr-lines for all the studied angles can be reproduced from the equation H-irr = H-0(Theta)(1 - T/T-c)(n), with n approximate to 4/3. From the angular dependence of H-0(Theta) parameter we estimated the anisotropy of the irreversibility lines. In the temperature interval [35, T-c] the anisotropy parameter was estimated gamma = H-irr(ab)/H-irr(c) = 2.2 +/- 0.1. The measurements of the real part of the fundamental (first harmonic) ac-susceptibility chi'(T) for constant temperature as a function of dc-magnetic field revealed, for high values of the ac-field amplitude, a second peak in the critical current. The second peak line is located far from H-irr-line and exists up to T-c. Although the particular sample has high critical densities, contrary to the predictions of the Bean's model, the maximum of the imaginary part of the fundamental ac-susceptibility chi '' exhibits lower values. This behavior could be explained by assuming a reversible motion of the flux lines around the pinning centers for low values of the ac-magnetic field amplitude. (C) 2012 Elsevier B. V. All rights reserved.

Dual-modality contrast agents, such as radiolabeled nanoparticles, are promising candidates for a number of diagnostic applications, since they combine the advantages of two different imaging modalities, namely SPECT or PET imaging with MR imaging. The benefit of such a combination is to more accurately interpret disease and abnormalities in vivo, by exploiting the advantages of each imaging technique, i.e. high sensitivity for SPECT/PET, high resolution anatomical information for MRI. In this review article, we provide an overview of recent findings in the synthesis, evaluation and application of radiolabeled iron oxide nanoparticles as dual-modality SPECT/MRI and PET/MRI imaging probes.

The structural and magnetic properties and spin dynamics of dextran coated and uncoated gamma-Fe2O3 (maghemite) nanoparticles have been investigated using high resolution transmission electron microscopy (HRTEM), Fe-57 nuclear magnetic resonance (NMR), Mossbauer spectroscopy and dc magnetization measurements. The HRTEM observations indicated a well-crystallized system of ellipsoid-shaped nanoparticles, with an average size of 10 nm. The combined Mossbauer and magnetic study suggested the existence of significant interparticle interactions not only in the uncoated but also in the dextran coated nanoparticle assemblies. The zero-field NMR spectra of the nanoparticles at low temperatures are very similar to those of the bulk material, indicating the same hyperfine field values at saturation in accord with the performed Mossbauer measurements. The T-2 NMR spin-spin relaxation time of the nanoparticles has also been measured as a function of temperature and found to be two orders of magnitude shorter than that of the bulk material. It is shown that the thermal fluctuations in the longitudinal magnetization of the nanoparticles in the low temperature limit may account for the shortening and the temperature dependence of the T-2 relaxation time. Thus, the low temperature NMR results are in accord with the mechanism of collective magnetic excitations, due to the precession of the magnetization around the easy direction of the magnetization at an energy minimum, a mechanism originally proposed to interpret Mossbauer experiments in magnetic nanoparticles. The effect of the surface spins on the NMR relaxation mechanisms is also discussed.

Core/shell particles were synthesized by assembling oppositely charged ferrite (Fe3O4 or NiFe2O4) nanoparticles on the surface of monodispersed silica core particles (having size similar to 0.4 mu m) prepared by hydrolysis and condensation of tetraethylortosilicate. Optimal conditions for synthesis of silica core/nano-Fe3O4 shell particles were found at pH similar to 5.4. The obtained particles have superparamagnetic behavior above a blocking temperature of approximate to 25 K, which make them very attractive for a broad range of biomedical and bioengineering applications. Incorporation of nickel into ferrite structure could not be achieved at lower pH value, so functionalization of core particles was required. Incorporation of nickel into ferrite structure was successful at pH above 7, however at higher pH the formation rate of nickel-ferrite particles becomes very fast and the self-aggregation dominates the competing formation of the nickel-ferrite shell. Because of that the self-aggregation was prevented by surface modification of nickel-ferrite nanoparticles with citric acid before their deposition on the functionalized silica core and homogenous and continuous NiFe2O4 shell was finally obtained. (C) 2012 Elsevier Ltd. All rights reserved.

Magnetic particles are currently applied to special biomedical and environmental applications owing to their unique magnetic, morphological and substance-carrying capabilities. Very recently we introduced Magnetically Assisted Hemodialysis (MAHD), an innovative therapeutic application of Ferromagnetic Nanoparticles (FNs) for the treatment of End-Stage Renal Disease (ESRD). MAHD can be employed for the selective and efficient removal of toxins that, although of high biological importance, they cannot be handled by current Hemodialysis strategies. This work is focused on evaluating the biocompatibility of Fe3O4 FNs with cells of donated human blood, namely Red Blood Cells (RBCs), White Blood Cells (WBCs) and Platelets (Pits). To that end, optical microscopy and atomic force microscopy were employed for the morphological examination of blood cells that were maturated under the presence of Fe3O4 FNs by means of mild incubation up to 120 min at T = 20 degrees C. As a conclusion we have not detected noticeable interference between RBCs, WBCs and Pits with FNs for the maturation conditions and the extreme FNs concentrations examined in this work.

In this paper we investigate the use of an epoxy bonded ferrimagnetic compound, Yttrium Iron Garnet (YIG), as a substrate of a patch antenna operating in Ku band. We investigate its influence on the antenna's polarization properties under the application of an external magnetic field. It is proved that the axial ratio and also the sense and the tilt of the antenna polarization ellipse are influenced by this substrate since they change in respect to the direction and the magnitude of an externally applied magnetic field. Also the presence of this material causes non reciprocal properties in the antenna operation, changing the antenna properties while in receiving or transmitting mode.

The paramagnetic Meissner effect (PME) is related to the appearance of a positive magnetization when a superconducting specimen is field cooled through its critical temperature. In this work we report on the PME and ac magnetization in roll-bonded Cu-Nb (RB/Cu-Nb) layered composites. We present typical DC magnetization loops obtained in the normal magnetic field configuration that show the PME. In addition, we present ac magnetization measurements that reveal a crossover behavior at a characteristic field value. We show evidence that such a crossover behavior, attributed to activation processes of vortices, is probably related to the disappearance of the PME in the RB/Cu-Nb layered composites.

One of the most significant challenges implementing colloidal magnetic nanoparticles in medicine is the efficient heating of microliter quantities by applying a low frequency alternating magnetic field. The ultimate goal is to accomplish nonsurgically the treatment of millimeter size tumors. Here, we demonstrate the synthesis, characterization, and the in vitro as well as in vivo efficiency of a dextran coated maghemite (gamma-Fe(2)O(3)) ferrofluid with an exceptional response to magnetic heating. The difference to previous synthetic attempts is the high charge of the dextran coating, which according to our study maintains the colloidal stability and good dispersion of the ferrofluid during the magnetic heating stage. Specifically, in vitro 2 mu l of the ferrofluid gives an outstanding temperature rise of 33 degrees C within 10 min, while in vivo treatment, by infusing 150 mu l of the ferrofluid in animal model (rat) glioma tumors, causes an impressive cancer tissue dissolution. (C) 2010 American Institute of Physics. [doi:10.1063/1.3449089]

CoPt and FePt compound films with L1(0) ordered structure have been intensively studied,due to their extremely high uniaxial magnetocrystalline anisotropy which makes them suitable for application in ultra high density magnetic recording media. A basic requirement in these type of media is the development of strong perpendicular magnetic anisotropy. The role of Ag underlayers in promoting strong (001) crystallographic texture and perpendicular magnetic anisotropy in post-annealed Ag/CoPt and Ag/FePt bilayers (BLs) has already been reported, along with a possible correlation between L1(0) formation and development of (001) crystallographic texture. In this work we present new data, which provide further evidence that there is indeed such a correlation during the annealing process of Ag/CoPt BLs. The most obvious manifestation of this correlation is the fact that the X-ray intensity ratios I-001/I-002 (used as a measure of the degree of L1(0)-ordering) and I-002/I-111 (used as a measure of the crystallographic texture) and the coercivity H-c and relative remnant magnetization m(r) (for field H normal to the surface of the films) exhibit the same kind of dependence from the thickness of the Ag underlayer. Comparison with respective crystallographic data from post-annealed Ag/CoPt nanocomposites (NCs) shows that in the case of NCs the (001) texture starts to degrade for lower total film thickness, compared to the case of BLs. This difference can be attributed to the structural incoherence in the growth of the CoPt grains imposed by the presence of Ag inside the Ag/CoPt NCs, while in BLs Ag is only used as an underlayer. Based on the above data and on detailed Heavy Ion Elastic Rutherford Back Scattering (HIRBS) measurements, performed on post-annealed Ag/CoPt NCs, we propose a possible mechanism for the interpretation of the observed correlation. The proposed mechanism is based on the reduction of total strain (residual strain of as-deposited film and transformation strain due to deformation of the unit cell as L1(0)-CoPt is formed) throughout the annealing process.

In this paper we introduce the incorporation of magneto-electric materials into antenna design and the potential of controlling the behavior of the antenna by means of an external magnetic field. After an intensive study of magneto-electric material properties, a ferrimagnetic compound called Yttrium Iron Garnet (YIG) was found to be the best candidate for the novel antenna design. We provide a metamaterial patch antenna design where a part of the substrate is replaced by the YIG compound. After several design modifications the final model includes a circular-shaped YIG substrate just under the metallic patch and offers sufficient performance in terms of resonance, bandwidth and radiation efficiency. Additionally, in the presence of an external magnetic field the polarization becomes elliptical and the sense of the polarization (left or right) can be controlled through the direction of the magnetic field. That latter characteristic confirms the metamaterial-nature of the antenna.

Background/Aims: Cell membranes facilitate the transport of water, ions, and necessary nutrients by hosting a great variety of transport channels that have either a 'simple' pore-like structure or more complex architecture that is based on the utilization of specific receptors. The present study reveals the impact of AgNO3, a well-known inhibitor of water channel activity, on transport channels that emerge at the membrane of intact red blood cells (iRBCs). Methods: Atomic force microscopy is employed to survey the morphological modification of all transport channels by directly comparing the respective images obtained on the exact same iRBCs prior to and after spraying the AgNO3 solution. Results: Small pores of mean size 50 nm that were assigned to water channels, and extended orifices of mean size 300 nm that exhibit a neck-like extracellular segment were observed at the iRBC membrane. Conclusion: Our results reveal that AgNO3 exerts noticeable influence on all transport channels so that its selective water channel inhibitory action should be reconsidered. For low AgNO3 concentrations extended recovery of the small pore network was observed upon waiting, giving strong evidence that iRBCs have a recovery potential upon simply removing the inhibition cause without the need for specific reducing agents. Copyright (C) 2009 S. Karger AG, Basel

In this paper we introduce the utilization of novel compounds that can be magnetoelectric, namely Al(2-x)FexO(3) and Ga2-xFexO3, or ferrimagnetic, namely Y3Fe5O12, as effective constituents in patch antennas. Owing to their coupled dielectric and magnetic properties these constituents can probably tune the radiation characteristics of the patch antenna by means of an externally controlled parameter such as a magnetic and/or electric field. We clearly demonstrate that using Y3Fe5O12 in the antenna substrate, the type and the sense of the antenna polarization is strongly influenced by applying an external magnetic field.

Iron oxide Ferromagnetic Nanoparticles (FNs) such as magnetite (Fe3O4) and maghemite (gamma-Fe2O3) are currently employed in biomedical applications owing to their relatively high biocompatibility. Recently, we have introduced a novel application of Fe3O4 FNs in the so-called Magnetically Assisted Haemodialysis (MAHD), a promising concept that can be employed for the treatment of End-Stage Renal Disease. The key characteristic of MAHD is the selective removal of toxins that cannot be removed by current low-and high-flux dialysers that are extendedly used during conventional Haemodialysis (HD). In addition, MAHD could enable the more efficient removal of all toxins when compared to conventional HD so that the duration of dialysis session could be decreased. This is an important benefit that could significantly improve the quality of life of patient. The present work focuses on the in vitro evaluation of the biocompatibility of both bare Fe3O4 FNs and Fe3O4-Bovine Serum Albumin Conjugates (Fe3O4-BSA Cs) with blood cells, namely Red Blood Cells (RBCs), White Blood Cells (WBCs) and Platelets (Plts). Their solubility in whole human blood medium is also carefully evaluated. Both issues are fundamental for the MAHD application since the latter is based on the intravenous injection of FN Cs into the bloodstream of the patient. Atomic force microscopy and optical microscopy were employed for the investigation of both surface characteristics and overall morphology of blood cells, respectively. Samples of donated blood, where bare Fe3O4 FNs or Fe3O4-BSA Cs were added, were maturated under mild incubation for durations up to 120 min. We investigated two representative temperatures, T=20 degrees C owing to easy experimental realization, and T=37 degrees C trying to simulate human body conditions. We did not observe noticeable interference of either bare Fe3O4 FNs or Fe3O4-BSA Cs with RBCs, WBCs and Plts. More importantly we did not observe any degradation of the surface of RBCs and WBCs that were maturated under the presence of bare FNs or Cs in concentrations that strongly exceed the ones used for the treatment of iron-deficiency anaemia. Incidents where either bare FNs or Cs were bound onto the surface of RBCs or internalised by WBCs were very rare. Our observations suggest high biocompatibility of both bare Fe3O4 FNs and Fe3O4-BSA Cs with blood cells, while the solubility depends on the BSA content of the Fe3O4-BSA Cs.

A commercially available powder of MgB2 is used as starting material for the examination of the influence of the annealing temperature on the properties of this intermediate-T-c superconductor. We performed scanning electron microscopy (SEM) and Hall ac-susceptibility measurements as a function of temperature and ac-field amplitude on samples annealed at 650, 750, 850 and 950 degrees C. The imaginary part of ac-susceptibility measurements is used to calculate both the inter-granular critical current density, J(c)(T-p) and density of pinning force, alpha(j)(0). It was observed that all T-c, J(c)(T-p) and alpha(j)(0) exhibit a non-monotonic behavior on the annealing temperature range studied in this work. T-c is measured to be 39.85 +/- 0.02 K and J(c)(T-p) is estimated to be as high as 60 A/cm(2) at 39.2 K for the sample annealed at 850 degrees C. The peak temperature, T-p, in the imaginary part of the ac-susceptibility curves shifts to lower temperatures with both decreasing the annealing temperature and increasing the amplitude of the ac-magnetic fields. A comparison of the experimental ac-susceptibility data with theoretical critical-state models that are currently available is performed. SEM investigations showed that the grain size increases, and the grain connectivity improves when the annealing temperature increases up to 850 degrees C. The possible reasons for the observed changes in transport, microstructure and magnetic properties due to annealing temperature are discussed. (C) 2009 Elsevier B.V. All rights reserved.

By means of magnetic measurements we have studied the magnetic properties of the NdFeAsO0.82F0.18 superconductor. We estimated the upper critical field H-c2(ab) (T) from the temperature at which the inverse magnetization deviates from linear behavior. Low field magnetic measurements revealed that a external magnetic induction of B = 0.01 T destroys the superconducting path between grains (weak-link behavior). Nd ions behave as isolated paramagnetic centers. This is evident since for magnetic inductions larger than 0.5 T a paramagnetic moment arises from the Nd that overcomes the superconducting diamagnetic signal. Hysteresis loops at several temperatures revealed that the critical current falls rapidly with temperature. The temperature variation of the reversible magnetization shows a behavior that is reminiscent of high-T-c cuprates, indicating the important role of thermal fluctuations.

Dialysis-related amyloidosis is related to the inefficient removal of beta(2)-microglobulin (beta(2)-m) that is mainly responsible for the formation of amyloid fibrils deposited on the joints and in the heart, blood vessels and digestive system. Magnetically assisted hemodialysis (MAHD) can be used for the prevention of dialysis-related amyloidosis. MAHD is based on ferromagnetic nanoparticle-targeted binding substance conjugates (FN-TBS Cs) that should be administered to the patient before the dialysis session. The TBS should have a high affinity for beta(2)-m so that the conjugates bind with the beta(2)-m in the bloodstream. The complex FN-TBS-beta(2)-m will be selectively removed during dialysis by means of a "magnetic dialyzer" that is installed at the dialysis machine in series to the conventional dialyzer. We have examined the in vitro applicability of MAHD by employing biocompatible Fe3O4 and bovine serum albumin (BSA) as constituents of the FN-TBS Cs. We evaluated the binding capacity of both bare Fe3O4 FNs and Fe3O4-BSA Cs for beta(2)-m concentrations ranging from mild to severe conditions. Finally, we conducted mock-dialysis experiments for the evaluation of several technical issues related to MAHD. beta(2)-m is adsorbed onto the Fe3O4-BSA Cs not only almost instantly, but also very efficiently. The employed Cs do not chemically interact with the materials used in standard dialyzers, as agglomerates were not observed in the capillaries of the conventional dialyzers. MAHD may become an efficient modality for the prevention of dialysis-related amyloidosis because beta(2)-m concentrations ranging from mild to severe conditions can be adequately handled.

Magnetically assisted hemodialysis is a development of conventional hemodialysis and is based on the circulation of ferromagnetic nanoparticle-targeted binding substance conjugates (FN-TBS Cs) in the bloodstream of the patient and their eventual removal by means of a 'magnetic dialyzer'. Presented here is an in vitro investigation on the biocompatibility of bare Fe3O4 FNs and Fe3O4-bovine serum albumin Cs with blood cells, namely red blood cells (RBCs), white blood cells (WBCs) and platelets (Plts). Atomic force microscopy (AFM) and optical microscopy (OM) enabled the examination of blood cells at the nanometer and micrometer level, respectively. The observations made on FN- and C-maturated blood samples are contrasted to those obtained on FN- and C-free reference blood samples subjected to exactly the same maturation procedure. Qualitatively, both AFM and OM revealed no changes in the overall shape of RBCs, WBCs and Plts. Incidents where bare FNs or Cs were bound onto the surface of RBCs or internalized by WBCs were very rare. Detailed examination by means of OM proved that impaired coagulation of Plts is not initiated/promoted either by FNs or Cs. Quantitatively, the statistical analysis of the obtained AFM images from RBC surfaces clearly revealed that the mean surface roughness of RBCs maturated with bare FNs or Cs was identical to the one of reference RBCs.

We propose a new method for the rejection of the comparatively strong diamagnetic contribution usually observed in SQUID magnetization measurements, originating from the substrates that are widely used for the preparation of thin magnetic films either by sputtering or by laser ablation techniques. Our method relies on the use of a substrate of length exceeding significantly the scan length employed in the magnetization measurements. Simple symmetry considerations reveal that the substrate's signal can be removed efficiently. This is also verified by a simple quantitative model, which is based on the form of total response of the four SQUID pick-up coils for a long sample. Our experimental data show clear evidence that the direct rejection of the substrate's undesired diamagnetic signal is complete in all the different categories of films (CoPt uniform single layers, CoPt isolated nanoparticles and La(1-x)Ca(x)MnO(3) multilayered specimens) studied in the present work. As a result, the real underlying mechanism that governs the physics of these magnetic films was uncovered. (C) 2008 Elsevier B.V. All rights reserved.

Owing to vast technological advances, hemodialysis (HD) has become a mature modality significantly increasing the survival of end-stage renal disease (ESRD) patients. However, many HD complications still exist that mainly relate to the nature of middle-molecular-weight and/or protein-bound toxins that both low- and high-flux dialysers cannot efficiently remove. For instance, hyperhomocysteinemia and amyloidosis are two dialysis-related disorders that motivate serious health complications. Here, we introduce a new method for the selective removal of specific toxins that is based on the preparation of Ferromagnetic Nanoparticle-Targeted Binding Substance Conjugates (FN-TBS Cs) constituted of biocompatible FNs and a specifically designed TBS that must have high affinity for the respective Target Toxin Substance (TTS). The FN-TBS Cs should be administered to the patient timely prior to the dialysis session so that they will be able to bind with the specific TTS owing to their free circulation in the bloodstream. The complex FN-TBS-TTS can be selectively removed from the ESRD patient during the HD session by means of a magnetic dialyser (MD). For the in vitro evaluation of this proposal we employed highly biocompatible Fe3O4 and Bovine Serum Albumin (BSA) as constituents of the FN-TBS Cs and an array of permanent magnets placed along the circulation line as a simple MD. We have evaluated the binding affinity and capacity of both bare Fe3O4 FNs and Fe3O4-BSA Cs by employing homocysteine (Hcy) as a model TTS. We investigate Hcy concentrations ranging from mild to severe hyperhomocysteinemia. Most importantly, we investigate the effectiveness of low concentrations of Fe3O4 that are within the safety levels established from the treatment of iron-deficiency anemia, thus making a preliminary evaluation of future in vivo applications. We observed that Hcy is readily adsorbed onto both bare Fe3O4 FNs and Fe3O4-BSA Cs. The obtained results prove the successful in vitro applicability of the proposed method since pathological Hcy concentrations may be adequately handled by relatively low Fe3O4 concentrations, thus making feasible future in vivo applications.

By using x-ray diffraction, magnetization and Mossbauer spectroscopy techniques we have studied the magnetoelectric Al2-xFexO3 (x = 0.8, 0.9 and 1.0) compound. Ac-susceptibility and magnetization measurements revealed magnetic transitions at T-N = 180, 210 and 260 K for x = 0.8, 0.9 and 1.0 respectively, that can be attributed to the Neel temperatures of ferrimagnetic to paramagnetic phase transition for all samples. Mossbauer spectra for the three samples were recorded between 4.2 and 295 K. Above the Neel temperature the paramagnetic spectra can be analyzed by three quadrupole doublets associated with the octahedral Fe1, Fe2 and Fe4 sites. The values of the hyperfine parameters show that iron ions are in the high spin Fe3+ state. The spectrum area of the doublet with larger quadrupole splitting increases with x, and in combination with x-ray diffraction results it can be attributed to the iron which occupies the Fe4 site. Below T-N(x) the Mossbauer spectra are magnetically split and at T = 4.2 K consist of six broad lines, indicating either a hyperfine magnetic field distribution (P(H-hyp)) or that the three octahedral sites give three unresolved sextets. The most probable value of H-hyp (the maximum value of P(H-hyp)) follows a power law indicative of a second order transition, in agreement with ac-susceptibility and magnetization measurements. The width of P(H-hyp) increases drastically toward low hyperfine magnetic fields as temperature increases. In addition, an appreciable percentage of the iron nuclei sense a hyperfine field with values in the interval [0, H-max]. This behavior can be explained by assuming that several magnetic sites with different superexchange parameters exist.

Background. The utilization of modern achievements from nanobiotechnology has resulted in novel modalities for renal replacement therapy. For conventional intermittent haemodialysis (HD), sophisticated membranes are currently being manufactured that guarantee selective removal of target toxins. These membranes have a narrow pore-size distribution that is focused around a mean value at the nanometre level. For continuous HD, novel artificial renal devices are currently being designed and evaluated in in vitro experiments that will be both implantable and have continuous function. Methods. We present mock-dialysis experiments using magnetically assisted HD (MAHD) that we very recently introduced for the selective removal of target toxins. MAHD is based on the preparation of conjugates (Cs) made up of biocompatible ferromagnetic nanoparticles (FNs) and a specifically designed targeted binding substance that must have a high affinity for a specific target toxin substance. The FN-targeted binding substance Cs should be administered to the patient prior to MAHD to allow for binding with the target toxin substance in the bloodstream. The complex FN-targeted binding substance-target toxin substance will then be removed by a 'magnetic dialyzer' that is installed in the dialysis machine in series to the conventional dialyzer. In the present work, we compared the in vitro efficiency of MAHD to conventional HD for the removal of homocysteine (Hcy) during mock-dialysis experiments. Results. These mock-dialysis experiments performed on Hcy revealed that both the removal rate and the overall removal efficiency of MAHD were significantly greater than conventional HD. Conclusions. MAHD appears to be a promising method that can be employed for the selective and more efficient extraction of toxins that are not adequately removed by conventional HD.

The present work describes the interfacial polymerization of aniline in the absence or presence of surfactants. Polyaniline was readily obtained in the semi-oxidized doped state and was cast from the aqueous phase. The structural and morphological characteristics of the polyanilines were deduced from X-ray Diffractometry and Scanning Electron Microscopy. Various morphologies were obtained depending on the surfactant addition. Conductivity measurements recorded for HCl doped polyaniline nanoneedles from 5 to 330 K showed a T, value at 230 K, where their transport behaviour changes from metallic-like above T, to semiconductive below T,. Furthermore, extensive magnetic measurements have been performed as a function of applied field and temperature. (c) 2007 Elsevier Ltd. All rights reserved.

In this work we study the transport properties of hybrids that consist of exchange biased ferromagnets (FMs) combined with a low-T-c superconductor (SC). Not only different FMs but also various structural topologies have been investigated: results for multilayers of La1-xCaxMnO3 combined with Nb in the form of [La0.33Ca0.67MnO3/La0.60Ca0.40MnO3](15)/Nb, and for more simple Ni80Fe20/Nb/Ni80Fe20 trilayers and Ni80Fe20/Nb bilayers are presented. The results obtained in all hybrid structures studied in this work clearly uncover that the exchange bias mechanism promotes superconductivity. Our findings assist the understanding of the contradictory results that have been reported in the recent literature regarding the transport properties of relative FM/SC/FM spin valves.

The vortex matter phase diagrams of aluminum doped Mg1-xAlxB2 crystals, deduced from local Hall ac-susceptibility (for H parallel to c axis) and bulk dc-magnetization measurements (for H parallel to c axis and ab plane) are reported. As in pristine and carbon doped MgB2, aluminum substituted crystals display the peak effect in the critical current. The peak effect is located very close to the H-c2(c)(T) line, while it disappears below a characteristic magnetic field H-* that depends on Al content. The absence of significant bulk pinning below the onset of the peak effect implies that the Bragg glass phase is present there. In some of the crystals the peak effect is not present as a sharp negative peak of the real part of the local ac susceptibility, but it appears as a negative double-peak feature. This observation may be related with the miscibility gap that occurs for 0.05 <= x <= 0.5. For low aluminum content the H-c2(c)(T) line lies slightly above the corresponding one of the pristine MgB2, but for higher aluminum content, T-c, H-c2(ab,c)(0), and anisotropy parameter gamma=H-c2(ab)(0)/H-c2(c)(0) take lower values when compared to pristine MgB2. Similarly with the pristine MgB2 crystals for the superconducting aluminum substituted crystals, the anisotropy parameter decreases monotonously as temperature increases as well. All the experimental observations could be qualitatively explained within the clean two-band approximation.

We report on the transport and magnetic properties of hybrid trilayers (TL's) and bilayers (BL's) that consist of low spin-polarized Ni80Fe20 exhibiting in-plane but no uniaxial anisotropy and low-T-c Nb. We reveal a magnetoresistance effect of magnitude identical to the ones that were reported in Pena [Phys. Rev. Lett. 94, 57002 (2005)] for TL's consisting of highly spin-polarized La0.7Ca0.3MnO3 and high-T-c YBa2Cu3O7. The presented effect is pronounced when compared to the one reported in Rusanov [Phys. Rev. B 73, 060505(R) (2006)] for Ni80Fe20-Nb-Ni80Fe20 TL's of strong in-plane uniaxial anisotropy. In our TL's the magnetoresistance exhibits an increase of two orders of magnitude when the superconducting state is reached: from the conventional normal-state values Delta R/R(nor)x100%=0.6% it goes up to Delta R/R(nor)x100%=45% (Delta R/R(min)x100%=1000%) for temperatures below T-c(SC). In contrast, in the BL's the effect is only minor since from Delta R/R(nor)x100%=3% in the normal state increases only to Delta R/R(nor)x100%=8% (Delta R/R(min)x100%=70%) for temperatures below T-c(SC). Magnetization data of both the longitudinal and transverse magnetic components are presented. Most importantly, we present data not only for the normal state of Nb but also in its superconducting state. Strikingly, these data show that below its T-c(SC) the Nb interlayer under the influence of the outer Ni80Fe20 layers attains a magnetization component transverse to the external field. By comparing the transport and magnetization data we propose a candidate mechanism that could motivate the pronounced magnetoresistance effect observed in the TL's. Adequate magnetostatic coupling of the outer Ni80Fe20 layers is motivated by stray fields that emerge naturally in their whole surface due to the multidomain magnetic structure that they attain near coercivity. Consequently, the stray fields penetrate the Nb interlayer and suppress its superconducting properties by primarily (secondarily) exceeding its lower (upper) critical field. Atomic force microscopy is employed in order to examine the possibility that such magnetostatic coupling could be promoted by interface roughness. Referring to the BL's, although out-of-plane rotation of the magnetization of the single Ni80Fe20 layer is still observed, in these structures magnetostatic coupling does not occur due to the absence of a second Ni80Fe20 one so that the observed magnetoresistance peaks are only modest.

It is generally believed that superconductivity and magnetism are two antagonistic long-range phenomena. However, as was preliminarily highlighted in Stamopoulos et al (2007 Phys. Rev. B 75 014501), and extensively studied in this work, under specific circumstances these phenomena instead of being detrimental to each other may even become cooperative so that their synergy may promote the superconducting properties of a hybrid structure. Here, we have studied systematically the magnetic and transport behavior of such exchange biased hybrids that are comprised of ferromagnetic (FM) Ni80Fe20 and low-T-c superconducting (SC) Nb for the case where the magnetic field is applied parallel to the specimens. Two structures have been studied: FM-SC-FM trilayers (TLs) and FM-SC bilayers (BLs). Detailed magnetization data on the longitudinal and transverse magnetic components are presented for both the normal and superconducting states. These data are compared to systematic transport measurements including I-V characteristics. The comparison of the exchange biased BLs and TLs that are studied here with the plain ones studied in Stamopoulos et al (2007 Phys. Rev. B 75 184504) enable us to reveal an underlying parameter that may falsify the interpretation of the transport properties of relevant FM-SC-FM TLs and FM-SC BLs investigated in the recent literature: the underlying mechanism motivating the extreme magnetoresistance peaks in the TLs relates to the suppression of superconductivity mainly due to the magnetic coupling of the two FM layers as the out-of-plane rotation of their magnetizations takes place across the coercive field where stray fields emerge in their whole surface owing to the multidomain magnetic state that they acquire. The relative in-plane magnetization configuration of the outer FM layers exerts a secondary contribution on the SC interlayer. Since the exchange bias directly controls the in-plane magnetic order it also controls the out-of-plane rotation of the ferromagnets' magnetizations so that the magnetoresistance peaks may be tuned at will. All the contradictory experimental data reported in the recent literature are discussed fairly in the light of our results; based on a specific prerequisite we propose a phenomenological stray-field mechanism that efficiently explains the evolution of the magnetoresistance effect in TLs. Our experiments not only point out the need for a new theoretical treatment of FM-SC hybrids but also direct us toward the design of efficient supercurrent-switch elemental devices.

The in vitro utilization of biocompatible ferromagnetic nanoparticles (BFNs) in hemodialysis (HD), routinely used today for the treatment of end stage renal disease (ESRD), is introduced in this work. The proposed strategy is termed magnetically assisted hemodialysis (MAHD) and it aims to become a more efficient development of conventional HD. The method is based on the production of biocompatible ferromagnetic nanoparticles-targeted binding substances conjugates (BFNs-TBSs Cs) constructed of BFNs and specifically designed TBSs that should have high affinity and binding capacity for target toxic substances (TTSs) which must be removed from the ESRD patient subjected to HD. Antibodies or even specific proteins could serve as the TBS of the desired BFNs-TBSs Cs. The BFNs-TBSs Cs should be administered to the patient timely prior to the MAHD session so as to bind with the desired TTSs during their free circulation in the vascular network. Eventually, the complete BFNs-TBSs-TTSs structure can be selectively removed during the MAHD session by means of an external inhomogeneous magnetic field that is applied either at the dialyzer or at other collection point(s) along the blood circulation line of the dialysis machine. The advantages of MAHD over conventional HD regarding the patient's comfort and overall health status are discussed in detail among practical issues. To examine this proposition we employed Fe3O4 and bovine serum albumin (BSA) as the BFN and the TBS constituents respectively, since they are both highly biocompatible. By means of x-ray diffraction, atomic force microscopy, circular dichroism spectropolarimetry, UV-vis spectrophotometry, SQUID magnetometry, and nuclear magnetic resonance we evaluated (i) the structural/morphological characteristics, (ii) the magnetic retraction efficiency, and most importantly (iii) the toxin binding affinity and capacity of both bare Fe3O4 BFNs and Fe3O4-BSA Cs by performing in vitro experiments on specific TTSs. Homocysteine and p-cresol were chosen as representative TTSs and were investigated in great detail. The results obtained prove the in vitro applicability of the proposed MAHD method.

By using nuclear magnetic resonance techniques we show that for T < 30 K the La0.875Sr0.125MnO3 compound displays a nonuniform charge distribution, comprised of two interconnected Mn ion subsystems with different spin, orbital, and charge couplings. The NMR results agree very well with the two spin wave stiffness constants observed at small q values in the spin wave dispersion curves [Phys. Rev. B 67, 214430 (2003)]. This picture is probably related to a yet undetermined charge and orbital superstructure occurring in the ferromagnetic insulating state of the La0.875Sr0.125MnO3 compound.

In the present work we study experimentally the influence that the domain structure of a ferromagnet (FM) has on the properties of a superconductor (SC) in bilayers and multilayers of La0.60Ca0.40MnO3/Nb and FePt/Nb proximity hybrids. Specific experimental protocols that were employed in the performed magnetization measurements enabled us to directly uncover a generic property of FM/SC hybrids: In the absence of an external magnetic field, the multidomain structure of the FM promotes the nucleation of superconductivity, while its monodomain state strongly suppresses it. Our experimental findings support recent theoretical studies [A. I. Buzdin and A. S. Mel'nikov, Phys. Rev. B 67, 020503(R) (2003); T. Champel and M. Eschrig, Phys. Rev. B 71, 220506(R) (2005)] that suggest the formation of the so-called domain-wall superconductivity and propose that when an inhomogeneous exchange field is offered by the FM to the SC the superconducting pairs are not susceptible to pairbreaking. In contrast, when magnetic homogeneity is restored in the FM the SC's properties are strongly suppressed.

In this work we study the modulation of superconductivity in combinatorial films (CFs) that are constructed by anisotropic CoPt ferromagnetic particles (FPs) randomly embedded in high-quality Nb layers of thickness 200 nm. In the constructed CFs the FPs are embedded in only half of the Nb layers. In this way we studied the modulation of superconductivity directly by performing transport measurements on the hybrid and pure superconducting areas of the CFs simultaneously under the application of the same dc current. Modulation of superconductivity and magnetic memory effects appeared only at the hybrid part of the CFs. This proves that superconductivity can be noticeably controlled under the action of the dipolar fields of FPs. The enhancement of the superconducting regime on the H-T operational diagram suggests that such hybrids can be attractive for current-carrying applications. In addition, magnetoresistive elemental superconducting devices could be based on our CFs. (c) 2005 Elsevier B.V. All rights reserved.

We studied by Mossbauer spectroscopy the Na0.82CoO2 compound using 1% 57 Fe as a local probe which substitutes for the Co ions. Mossbauer spectra at T = 300 K revealed two sites which correspond to Fe3+ and Fe4+. The existence of two distinct values of the quadrupole splitting instead of a continuous distribution should be related with the charge ordering of Co+3, Co+4 ions and ion ordering of Na(1) and Na(2). Below T = 10 K part of the spectrum area, corresponding to Fe4+ and all of Fe3+, displays broad magnetically split spectra arising either from short-range magnetic correlations or from slow electronic spin relaxation. (c) 2006 Elsevier Ltd. All rights reserved.

The vortex-matter phase diagram of Tl2Ba2CaCu2O8+x single crystal superconductor has been studied, using bulk and local magnetization measurements. We observed a second magnetization peak in the temperature interval 20 K < T < 40 K. At 40 K the second peak splits into two peaks, termed the upper and lower second magnetization peaks (USP and LSP), respectively. In the magnetic field interval [H-LCP,H-UCP] we observed the clear signature of a first-order melting transition of the vortex lattice. This particular behavior is similar to a situation with two critical endpoints of the first-order melting line and one coexistence point, where the topological transition line ends on the first-order melting line.

The vortex matter phase diagram for H parallel to c of the thallium-based cuprate with formula Tl2Ba2CaCu2O8 (Tl-2212) has been studied using magnetization measurements. We observed a second magnetization peak monotonically decreasing with temperature in the temperature interval 20 K < T < 40 K. At 40 K the second peak splits into two peaks. The field location of the lower part of the second peak decreases with temperature and for 80 K <= T <= T-c it is transformed to a sudden drop. The corresponding upper part of the second peak forms a broad maximum and subsequently develops a negative curvature as it approaches the melting line. In the magnetic field interval [H-LCP,H-UCP] we observed a first-order melting transition (FOT) of the vortex lattice. (c) 2006 Elsevier B.V. All rights reserved.

The influence of the structural quality of a normal metal-superconductor interface on the strength of the proximity effect is studied for the cylindrical geometry of bulk Cu-Nb multifilamentary composite samples. In as-drawn Cu-Nb samples the superconducting properties induced to the Cu matrix due to its proximity with Nb filaments are manifested in the magnetization measurements through a pronounced peak positioned in the low-field regime. By systematic annealing in an extended temperature regime for various durations we changed the structural quality of the Cu-Nb interfaces and as a result their transparency to the superconducting carrier. The direct comparison of scanning electron microscopy images with magnetization data revealed that the distortion of the Cu-Nb interfaces is responsible for the suppression of the proximity effect. (c) 2006 Elsevier B.V. All rights reserved.

We report on the influence of the microstructure on the AC and DC magnetic properties of Cu-3.5% Nb nanofilamentary wires. Samples obtained from a single Cu-3.5% Nb wire were subsequently submitted to different plastic strain levels via drawing so that their microstructure was altered. Noticeable differences are observed in their isothermal DC magnetization curves that present a double-peak structure. The first peak, which occurs at low magnetic fields, is attributed to superconductivity induced in the Cu matrix due to the proximity effect. It is argued that the second peak is related exclusively to niobium. The dependence of these two distinct peaks on the characteristic nanometre length scales of the samples, i.e. dimension of the Nb filaments and interfilamentary spacing, are discussed.

We report on the microstructure evolution in Cu-15% Nb multifilamentary wires upon annealing and the corresponding effects on their electrical and magnetic properties. During annealing at temperatures higher than 800 degrees C thermal instability mechanisms take place in the microstructure of the Cu-15%Nb composite, leading to spheroidization, followed by coarsening of niobium filaments. Such microstructural changes exert considerable influence on the magnitude of the normal electrical resistivity for the Cu-Nb composite. In addition, the annealing process leads to a double-peak structure in the isothermal DC magnetization curves of the composite, which is strongly dependent on the annealing time. This behavior suggests that the spheroidization kinetics can be obtained from M(H) curves.

In the present work we study extensively the manipulation of superconductivity through ferromagnetism in a new category of hybrids. The studied hybrids consist of antiferromagnetic/ ferromagnetic (AF/FM) [La0.33Ca0.67MnO3/La0.60Ca0.40MnO3](15) multilayers (MLs) in contact with a low-T-c Nb superconductor (SC). In these hybrids a relatively thick FM buffer layer was used as a reservoir for the generation of stray fields that influence the SC intensively. Our results show that in the parallel field configuration the SC becomes ferromagnetically coupled to the ML when field-cooled through its T-c(SC). Thus, although the SC should behave diamagnetically in respect to the externally applied magnetic field, its bulk magnetization behaves ferromagnetically and switches together with the magnetization of the ML when its coercive field is exceeded (switching effect). By employing specific experiments, where the ML was selectively exchange biased or not, we clearly demonstrate that the ML structure, separating the FM buffer and the SC layers, inflicts its magnetic properties on the whole hybrid. Thus, in such ML/SC hybrids the exchange bias mechanism can be used for regulating the switching of the SC magnetization. By employing specific experimental protocols for our magnetization measurements we directly uncover that the multidomain magnetic state of the ML strongly suppresses both the transition's height and the critical temperature of the SC. Simple FM/SC bilayers have also been studied. In these samples the switching effect is observed only for zero external field, while it is absent when a magnetic field is applied. This indicates that the ML structure is an essential ingredient for the generic observation of the switching effect. Our experimental results support recent theoretical studies referring to the mutual proximity effect (Kharitonov et al 2006 Phys. Rev. B 73 054511), to the possible formation of spin-triplet superconductivity (Bergeret et al 2001 Phys. Rev. Lett. 86 4096), and to the influence of an FM domain state on the properties of an SC (Buzdin and Mel'nikov 2003 Phys. Rev. B 67 020503( R)) in relevant hybrids. Apart from their importance for theory, our results are valuable for the design of spin-valve devices that recently have attracted great interest.

Nucleophilic substitutions of the reactive chlorine atoms in cyanuric chloride by the bridging 4,4'-bipyridine in refluxing toluene lead to quaternarization of the latter and the subsequent formation of a pi-conjugate, covalent layered network. The network is composed of central 1,3,5-triazine units with 4,4'-bipyridinium rings covalently attached and balanced by the released chloride ions. Due to the extremely high electron deficiency of the triazine rings, the material undergoes partial reduction by its compensated chloride ions resulting in a radical concentration of 1 X 1020 spin g(-1), according to EPR quantitative analysis. In this instance, the radicals provide stability to the organic network by minimizing its electron deficiency. The material exhibits thermal and electrochemical stability, as evidenced by thermal gravimetric analysis (TGA) and cyclic voltammetry techniques. As such, the pi-conjugate organic material displays low band gaps and electrical conductivity in the range of 10(-4)-10(-5) S cm(-1) at room temperature. (c) 2006 Elsevier Ltd. All rights reserved.

Model combinatorial films (CFs) which host a pure superconductor adjacent to a ferromagnetic-superconducting hybrid film (HF) are manufactured for the study of the influence of ferromagnetic nanoparticles (FNs) on the nucleation of superconductivity. Careful resistance measurements were performed simultaneously on two different sites of the CFs. Enhancement of superconductivity and magnetic memory effects were observed only on the hybrid site of the CFs but were absent on their purely superconducting part. Our results give direct proof that the FNs modulate the superconducting order parameter in an efficient and controlled way giving us the possibility of miscellaneous practical applications.

The nucleation of superconductivity in a hybrid film (HF) that consists of randomly distributed CoPt ferromagnetic nanoparticles (FNs) embedded in a 200 nm Nb layer was studied by combined magnetic and magnetoresistance measurements. The FNs exhibit both soft and hard magnetic behaviour. It is found that both magnetic phases contribute to the modulation of bulk and surface-like superconductivity by broadening their intermediate regime. More specifically, while the soft FNs (SFNs) promote bulk superconductivity, the hard FNs (HFNs) suppress the bulk superconducting state. In contrast, both SFNs and HFNs promote surface-like superconductivity since on the H-T phase diagram the respective boundary line presents abrupt upturns at their corresponding saturation fields. The dependence of the observed effects on the magnetic history gives clear evidence that they are mainly induced by the cooperative action of the FNs. Our experimental results are compared with current theoretical studies on relevant hybrid systems. Finally, the possible applications that such HFs could find in the near future are discussed.

We studied the crystal and magnetic structure of the La1-xCaxMnO3 compound for (0.11 <= x <= 0.175) using stoichiometric samples. For x < 0.13 the system's ground state is insulating canted antiferromagnetic. For 0.13 <= x <= 0.175 below the Jahn-Teller transition temperature (T-JT) the crystal structure undergoes a monoclinic distortion. The crystal structure can be described with P2(1)/c space group which permits two Mn sites. The unit-cell strain parameter s=2(a-c)/(a+c) increases for T < T-JT, taking the maximum value at the Curie point, and then decreases. Below T-M'M''approximate to 60 K s abruptly changes slope and finally approaches T=0 K with nearly zero slope. The change of s at T-M'M'' is connected to a characteristic feature in the magnetic measurements. As x increases towards the ferromagnetic metallic boundary, although s is reduced appreciably, the monoclinic structure is preserved. The monoclinic structure is discussed with relation to the orbital ordering, which can produce the ferromagnetic insulating ground state. We also studied samples that were prepared in air atmosphere. This category of samples shows ferromagnetic insulating behavior without following the particular variation of the s parameter. The crystal structure of these samples is related to the so-called O-* (c > a > b/root 2) structure.

In this paper we demonstrate the dependence of MgB2 as for its superconducting properties with respect to different thermal profiles used at the manufacturing stage of the compound. A colligation is made between the change of the superconducting capabilities and the structure of the final material. The samples were characterized, as far as the structure is concerned, with an X-ray diffractometer, a scanning electron microscope, and a differential thermal analyzer. As for the superconductivity aspect of the compound, the dependence of the magnetic ac susceptibility and resistivity with respect to temperature was determined. (c) 2004 Elsevier B.V. All rights reserved.

In this work we present magnetization data on hybrids consisting of multilayers (MLs) of manganites [La0.33Ca0.67MnO3/La0.60Ca0.40MnO3](15) in contact with a low-T-c Nb superconductor (SC). Although a pure SC should behave diamagnetically in respect to the external magnetic field in our ML-SC hybrids we observed that the magnetization of the SC follows that of the ML. Our intriguing experimental results show that the SC below its T-c(SC) becomes ferromagnetically coupled to the ML. As a result in the regime where diamagnetic behavior of the SC was expected its bulk magnetization switches only whenever the coercive field of the ML is exceeded. By employing specific experiments where the ML was selectively biased or not we demonstrate that the ML inflicts its magnetic properties on the whole hybrid. Possible explanations are discussed in connection to recent theoretical proposals and experimental findings that were obtained in relative hybrids.

We report on the microstructural evolution in Cu 15%Nb multifilamentary wires upon annealing and the corresponding effects on their magnetic properties. During annealing at temperatures higher than 800 degrees C thermal instability mechanisms take place in the microstructure of the Cu 15 %Nb composite, leading to the spheroidization of niobium filaments. Another important consequence of annealing is the recrystallization of Nb, that has a straightforward influence on the magnetization data. When compared to the as-drawn composite, in the annealed Cu15%Nb samples the bulk upper critical field H-c2(T) is reduced significantly, while the lower critical field H-c1 (T) is increased as a function of the annealing temperature and time. This indicates that we may employ this process as an efficient method to modify the basic superconducting parameters of Nb, namely the coherence length (T) and the penetration depth lambda(T).

We report on magnetic and magnetoresistance measurements in two categories of superconducting Nb films grown via magnetron sputtering and MgB2 bulk samples. In the first category, films of T-c = 9.25 K were produced by annealing during deposition. In these films, the magnetic measurements exhibited the so-called 'second magnetization peak' (SMP), which is accompanied by thermomagnetic instabilities (TMI). The characteristic field H-fj, where the first flux jump occurs, has been studied as a function of the sweep rate of the magnetic field. Interestingly, in the regime T < 6.4 K, the respective line H-fj(T) is constant, H-fj(T < 6.4 K) = 40 Oe. A comparison to TMI observed in MgB2 bulk samples is also performed. Our experimental findings cannot be described accurately by current theories on TMI. In the second category, films of T-c = 8.3 K were produced without annealing during deposition. In such films, we observed a peak effect (PE). In high magnetic fields the PE is accompanied by a sharp drop and a narrow hysteretic behaviour (DeltaT < 20 rnK) in the measured niagnetoresistance. In contrast to experimental works presented in the past, the comparison of our magnetic measurements with the magnetoresistance data suggests that the appearance of surface superconductivity rather than the melting transition of vortex matter is the cause of the observed behaviour.

We report on combined resistance and magnetic measurements in a hybrid structure (HS) of randomly distributed anisotropic CoPt magnetic nanoparticles (MN) embedded in a 160 nm Nb thick film. Our resistance measurements exhibited a sharp increase at the magnetically determined bulk upper-critical fields H-c2(T). Above these points the resistance curves are rounded, attaining the normal state value at much higher fields identified as the surface superconductivity fields H-c3(T). When plotted in reduced temperature units, the characteristic field lines H-c3(T) of the HS and of a pure Nb film, prepared at exactly the same conditions, coincide for H<10 kOe, while for fields H>10 kOe they strongly segregate. Interestingly, the characteristic value H=10 kOe is equal to the saturation field H-sat(MN) of the MN. The behavior mentioned above is observed only for the case where the field is normal to the film's surface, while it is absent when the field is parallel to the film. Our experimental results suggest that the observed enhancement of surface superconductivity field H-c3(T) is possibly due to the not uniform local reduction of the external magnetic field by the dipolar fields of the MN.

By using isothermal magnetization measurements in polycrystalline MgB2 samples, we estimate the H-c2(c) in the interval [0, T-c]. By combining these measurements to the estimated H-c2(ab) from the onset of the diamagnetic transition in isofield and isothermal magnetic measurements, an estimation of the anisotropy parameter can be achieved. The H-c2(c) values coming from high quality polycrystalline samples agrees nicely to those obtained on single crystals. Our results show a temperature variation of the gamma(T) = H-c2(ab) / H-c2(c) with gamma(T-c) approximate to 3.

We report on magnetic measurements as a function of field, temperature and time (relaxation) in superconducting Nb films of critical temperature T-c = 9.25 K. The magnetic measurements as a function of field exhibited a "second magnetization peak" (SMP) which in general is accompanied by thermomagnetic instabilities (TMIs). The lines H-smp(T) where the SMP occurs and the H-fj(T) where the first flux jump in the virgin magnetization curves is observed, end at a characteristic point (T-0, H-0) approximate to (7.2K, 80 Oe). Relaxation measurements showed that for T < T-0 approximate to 7.2 K the activation energy U-0 and the normalized relaxation rate S exhibit non-monotonic behavior as a function either of temperature or field. The extrema observed in U-0 and S coincide with the points H-on(T) or H-smp(T) of the SMP. In the regime T > T-0 approximate to 7.2 K both U-0 and S present a conventional monotonic behavior. These results indicate that the SMP behavior observed in Our Nb films is promoted by the anomalous relaxation of the magnetization. (C) 2004 Elsevier B.V. All rights reserved.

We have studied the vortex matter phase diagram in two carbon doped MgB2-xCx (x=0.04 and 0.1) single crystals. We have found that, as in pristine MgB2, the peak effect is also present in carbon doped crystals. The regime where the peak effect is developed is more extended in comparison to the undoped crystal. The enhancement of the peak effect regime, combined with the higher H-c2(c)(0), makes doped MgB2 more favorable for practical applications. The absence of significant bulk pinning below the line H-on(T), which denotes the onset points of the peak effect, implies that the Bragg glass phase is present for H

By means of local Hall probe ac and dc permeability measurements, we investigate the phase diagram of vortex matter for the HgBa2CuO4+delta superconductor in the regime near critical temperature. The second peak line H-sp, in contrast to what is usually assumed, does not terminate at the critical temperature. Our local ac permeability measurements reveal a pronounced hysteretic behavior and thermomagnetic history effects near the onset of the second peak, giving evidence of a phase transition of vortex matter from an ordered qausilattice state to a disordered glass.

We report on the second peak line H-sp and the possible phases of vortex matter near T-c for a detwinned underdoped YBa2Cu3O7-delta single crystal. Our local ac and dc permeability measurements revealed that the second peak line H-sp does not terminate either at the critical temperature or on the irreversibility line H-irr. Pronounced hysteretic behavior is observed in the regime below the second peak line H-sp. Below (above) a characteristic field the end point of the second peak differs from (coincides with) the irreversibility point, H(end point)not equalH(irr) (H(end point)equivalent toH(irr)). A possible reentrance of a dynamically ordered solid phase in the high-temperature regime near the irreversibility line is discussed.

Local Hall probe ac permeability and global dc SQUID magnetization measurements were used to construct the phase diagram of the vortex matter for two HgBa2CuO4+delta single crystals with different amounts of disorder. Emphasis was given near T-c and for low magnetic fields H-dc < 1 kOe. For the nearly optimally doped crystal with T-c = 94.8 K, the second peak line H-sp and the respective onset line H-min of the magnetization loops end at (T*, H*) = (88 K, 2 kOe) on the irreversibility line, while for the crystal of lower T-c (= 89.9 K) decreases monotonically and terminates just below T-c In addition, for the crystal with T-c = 89.9 K the local permeability measurements (as a function of temperature or dc magnetic field) revealed a peak in the screening current just below the onset of the diamagnetic screening. The possible sublimation character of the melting transition, the two-stage melting scenario and a Bragg to vortex glass transition are discussed. The different behaviours observed between the two crystals is attributed to the different amount of disorder.

The local ac and dc magnetic response in an untwinned YBa2Cu3O7-delta crystal has been measured using a microscopic Hall sensor. Due to the low pinning energy at elevated temperatures (near T-c), the ac response of the platelet-shaped crystal is governed by the geometrical barrier. From the field where the first vortex penetrates into the center of the crystal we estimated the first critical field (H-c1). The temperature variation of H-c1 near T-c is compatible with a strongly type-H superconductor, where the fluctuations in the order parameter (Psi) are those of an uncharged superfluid of the three dimensional XY model. In order to extract a reasonable value for the London penetration length at T=0 K, a value c(0)=3 is needed for the core contribution of the line energy of the vortex.

In this work we report on the crystal growth process, the crystal structure and the phase diagram of HgBa2CuO4+chi high T-e superconductor. Precise global DC magnetization measurements, using a SQUID magnetometer, have been performed, on two single crystals in magnetic fields parallel to the c-axis (H \ \ c) with T-c = 95 and 89.9 K, respectively. The irreversibility curve H-irr(T) decreases exponentially up to a temperature T* and after it changes slope abruptly. The magnetization curves at a fixed temperature as a function of magnetic field show two peaks, namely H-fp(T) and H-sp(T). (C) 2001 Elsevier Science B.V. All rights reserved.

We present a modified method of preparation of the new superconductor MgB2. The polycrystalline samples were characterized using X-ray and magnetic measurements. The surface barriers control the isothermal magnetization loops in powder samples. In bulk as prepared samples we always observed symmetric magnetization loops indicative of the presence of a bulk pinning mechanism. Magnetic relaxation measurements in the bulk sample reveal a crossover of surface barrier to bulk pinning.

The magnetic critical behavior in the series La-0.67(BaxCa1-x)(0.33)MnO3 (0 less than or equal to x less than or equal to 1) of manganese perovskites is studied by means of DC magnetic measurements. As Ca ions are substituted by the larger Ba ions, the transition temperature increases from 265 to 340 K as a result of structural changes. Arrott plots show that only in samples with x greater than or equal to 0.25 the magnetic properties follow the behavior expected for a conventional second-order ferromagnetic transition. The values of critical exponents (beta, gamma) estimated by modified Arrott plots are found to lie between those predicted for a 3D-Heisenberg model and those of mean field theory. (C) 2000 Elsevier Science B.V. All rights reserved.

Local Hall dc-susceptibility and global dc-magnetization measurements are used in order to construct the vortex matter phase diagram for a HgBa2CuO4+x single crystal with T similar to 89.9 K. For T > T* = 82 K, the points where the step in rile local ac-susceptibility measurements and the anomaly in the de magnetization measurements occur fall on the same curve, indicating that the same phenomenon is observed in both cases. We modeled these points by a power law H-m(T) = H-o(1-T/T-c)(a), with a = 2.4 +/- 0.1 and H-o = 267 +/- 125 kOe. The local Nail ac-susceptibility data, below the "step" temperature, show a behavior which can be explained if we suppose that at the vicinity of the step a local peak in the J(c)(T) curve exists (so-called peak effect). (C) 2000 Elsevier Science B.V. All rights reserved.

We performed magnetic moment (m) relaxation measurements at low temperatures (5 less than or equal to T less than or equal to 20 K) in two single phase, c-axis-oriented polycrystalline Bi1.7Pb0.3Sr2Ca2Cu3O10+delta (2223) samples prepared under different conditions with different T-c's. The m versus t data show a logarithmic relation and by fitting them the J(c)(H, T) and U-c(H, T) variation were extracted. (C) 2000 Elsevier Science B.V. All rights reserved.

The relaxation of the magnetic moment of a thin disk of YBa2Cu3O7-delta superconductor in a perpendicular magnetic field shows a logarithmic dependence on time for the examined temperature range T: 10-60 K. Data are analyzed within an analytical model. The temperature dependencies of the critical current j(c), and the pinning potential U-0, are estimated by fitting the relaxation data. Furthermore, the E versus j characteristics are quantitatively derived from the relaxation data at the circumference of the disk. (C) 2000 Elsevier Science B.V. All rights reserved.

We used local AC-susceptibility and global DC magnetization measurements to determine the magnetic phase diagram of two HgBa2CuO4+delta single crystals with T-c = 95 and 89.9 K, respectively. The corresponding lines for the more anisotropic crystal (T-c = 89.9 K, crystal A) lie lower than those of the nearly optimally doped crystal (T-c = 95 K, crystal B). The irreversibility line (IL) decreases exponentially in the temperature range 20 less than or equal to T less than or equal to T*. At T* = 82 and 88 K the IL change slope and varies with a power law up to the T-c. Certain features in these measurements are also discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

The irreversibility magnetic field H-irr(T) decreases exponentially in the temperature range 20 less than or equal to T less than or equal to 88 K. At T* approximate to 88 K, the H-irr(T) curve changes slope abruptly and a new mechanism controls the irreversibility up to T-c. The hysteresis loops measurements (H parallel to c) show a second peak for 5 less than or equal to T less than or equal to 50 K. Relaxation measurements performed in the region of the second peak show, at constant temperature, that effective activation energy U-o(H) first increases up to H-sp'(T) and then decreases for H > H-sp'(T). H-sp'(T) is located lower than the field H-sp(T) deduced from the hysteresis loops. (C) 1999 Elsevier Science B.V. All rights reserved.

The temperature and magnetic-field dependence of activation energy U-o(T,H) for creep has been studied in an HgBa2CuO4+delta single crystal below and above the "fishtail" peak H-sp(T). At constant temperature, U-o(H) increases up to H-sp'(T) and then for H>H-sp'(T) it decreases. H-sp'(T) is located lower than the field H-sp(T) deduced from the hysteresis loops. The decrease of the activation energy is probably indicative of a plastic-type creep of the vortex lattice. We demonstrate that the overall behavior of U-o(T,H) at the second magnetization peak line H-sp(T) in the phase diagram of HgBa2CuO4+delta exhibits similarities with that observed in Bi2Sr2CaCu2O8+delta and YBa2Cu3O6.95 compounds. [S0163-1829(99)04018-7].