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 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.

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.

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 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.