The EPR spectrum of the oxygen-deficient Sm0.5Er0.5Ba2Cu3O6+x mixed phase has been investigated in the temperature range of 3.3-20 K. Anomalous behavior of the EPR spectrum has been detected below 4 K that may indicate the presence of magnetic centers with singlet ground state and an excitation energy of the order of 1 K. © 2000 Elsevier Science B.V. All rights reserved.

The temperature dependence of the EPR spectra for the oxygen deficient Ni2 FeVO6-δ compound has been investigated in the range of 50-300 K. An intense EPR line associated with high-spin iron centers or ferromagnetic clusters, is observed. The strong temperature dependence of the EPR intensity, resonance field and line width is consistent with the stepwise magnetization variation and supports the presence of successive magnetic anomalies at lower temperatures. © 2000 Elsevier Science B.V. All rights reserved.

The potential of photoacoustic spectroscopy to resolve the crystal field levels of Cu2+ ions in three polyamine copper complexes, aqua spermine copper sulfate trihydrate [NH2(CH2)3NH(CH2)4NH(CH2)3 NH2·Cu2+·H2O]·SO42-·3H2O, norspermine copper sulfate trihydrate [NH2(CH2)3NH(CH2)3NH(CH2)3 NH2·Cu2+·SO42-]·3H2O, and homospermine copper sulfate dihydrate [NH2(CH2)3 NH(CH2)2NH(CH2)3 NH2·Cu2+·SO42-]·2H2O, has been explored along with UV/VIS and electron paramagnetic resonance (EPR) spectroscopy. Intense absorption is detected in the photoacoustic spectrum corresponding to the d-d transition band weakly traced in the corresponding optical spectrum. The observed fine structure photoacoustic lines are assigned to the individual d-d transitions of Cu2+ ions, which are further exploited to determine the diverse metal-ligand interaction of the studied compound employing simple crystal field analysis.

Voltage-modulated scanning force microscopy is applied to study the temperature dependence of the ferroelectric domain structure of triglycine sulfate up to TC, the ferroelectric transition temperature. The polarization image contrast exhibits a power-law decrease as TC is approached, associated with the competition between Maxwell stress and the converse piezoelectric effect. Substantial differences in the static and dynamic domain patterns are detected for two samples of different aging conditions. © 2000 American Institute of Physics.

Voltage-modulated scanning force microscopy has been applied to investigate domain kinetics in triglycine sulfate single crystals, thermally quenched from the paraelectric to the ferroelectric phase. Temporal analysis of the equal-time correlation functions shows that the average domain size grows initially with a power law dependence close to that of conserved systems, whereas a crossover to the slower logarithmic growth law (Formula presented) predicted for systems with random impurities occurs in the late stage of coarsening. Domain growth is dominated by a single characteristic length scale consistent with the dynamical scaling hypothesis. The total surface charge corresponding to the domain area of the two polarization states is found to be conserved within the studied time scale, indicating that the system may be considered to behave like one with conserved order parameter. © 2000 The American Physical Society.

Contrast mechanisms for the detection of antiparallel domains in ferroelectric materials such as triglycine sulfate are investigated in the dynamic contact electrostatic force microscope. The domain contrast exhibits strong dependence on voltage modulation frequency, which is explained with the excitation of resonant modes of the cantilever in contact conditions. Phenomena such as contrast enhancement, inversion, and nulling are detected and accounted for with a simple model for the tip-sample interaction. The model includes the effects of the viscoelastic sample response and confirms that the observed contrast features have to be attributed to the spectral response of the tip-sample junction. © 2000 The American Physical Society.

Oxygen deficient ErxY1-xBa3Cu26+y (x=1.0, 0.5) compounds are studied by EPR spectroscopy. The EPR spectra reveal the presence of high spin (S>1) paramagnetic centers, dimers and free Cu2+ ions, which appear enhanced in the mixed R phase and suppressed in the single R123 one, consistent with phase separation. © 2000 Elsevier Science B.V. All rights reserved.

Oxygen deficient La0.5Gd0.5Ba2Cu3O6+x has been studied by EPR spectroscopy. The temperature dependence of EPR spectrum reveals the presence of sustained magnetic ordering of the Gd3+ sublattice and localized paramagnetic centers corresponding to copper-oxygen clusters. © 2000 Elsevier Science B.V. All rights reserved.

Voltage-modulated scanning force microscopy has been employed to investigate the dynamics of ferroelectric domains as a function of time and temperature in triglycine sulfate (TGS) single crystals. Branching of the domain structure and nucleation of fine domain patterns by internal fields of thermal origin have been directly observed on the submicron scale. Domain coarsening after quenching TGS samples from the paraelectric phase into the ferroelectric one has been studied, revealing a nonlinear time dependence of the characteristic correlation domain length and supporting the validity of dynamical scaling law and the conservation of the total surface charge. Substantial differences in the evolution of the domain structure have been detected during cooling or heating treatment in the ferroelectric phase. Domain contrast is shown to monitor the ferroelectric phase transition through its temperature dependence, reflecting the competition between electrostatic and piezoelectric effects. © 2000 American Institute of Physics.