Observation of anomalous dissipation in dynamics of vortices in Bi2212 in the region of 3D-2D crossover

Anomalous decrease of the amplitude of Bi 2212 single-crystal vibrations in magnetic field is observed, indicating the existence of strong damping in vortex matter in the region of 3D-2D crossover. This phenomenon occurs in the temperature region 5–35 K and at magnetic fields of 500–1500 Oe where the second-peak effect in magnetization is observed. The results are in qualitative agreement with the Monte Carlo simulation of phase transitions in a vortex system

Local probing of magnetoelectric coupling in multiferroic composites of BaFe12O19-BaTiO3

The BaFe12O19-BaTiO3 composite ferroelectric/ferromagnetic ceramics were prepared by conventional solid-state sintering technique. The magnetic properties are consistent with the ratio of the magnetic phase present but ferroelectric properties are degraded due to a sufficiently high degree of conductivity in the ceramics. Magnetoelectric coupling was observed at a local level by means of the scanning probe microscopy (SPM). Piezoresponse and magnetic force modes of SPM were both utilized to assess strain-mediated magnetoelectric coupling between neighboring grains. The observed variation in the magnetic signal after the electrical poling with SPM was attested to the changes in the magnetic interactions and magnetic anisotropy leading to broadening of the magnetic domain wall. © 2010 American Institute of Physics

Preparation, Structural and Electrophysical Studies of Ferroelectric Ceramic Samples of the System (1-2x)BiScO3-xPbTiO3-xPbMg1/3Nb2/3O3, 0 ≤ x ≤ 0.50

Ceramic samples of the (1-2x)BiScO3-xPbTiO3-xPbMg1/3Nb2/3O3 system in the whole compositions region x = 0-0.50 were synthesized. According to the X-ray diffraction studies (XRD), the region of solid solutions with perovskite structure formation in the system was determined (x = 0.23-0.50). The presence of a morphotropic phase boundary between tetragonal and rhombohedral forms of solid solutions was established at x = 0.40-0.42. Refined XRD with profile peak analysis established the presence of the additional cubic phase with broadened X-ray reflexes in the solid solutions along with the main phase. It was concluded that the main and additional phases are located in the volume and in the surface layer of ceramic crystallites, respectively. The crystal structures of phases in the polarized and depolarized sample with x = 0.42 were determined by the Rietveld method. It was found that the monoclinic perovskite phase is present in the polarized sample. Temperature-frequency dependences of dielectric permittivity and losses of solid solutions were studied. It was found that the increasing content of BiScO3 in samples causes a change in their dielectric properties from the usual ferroelectric (FE) in the region (1-2x) = 0-0.08 to ferroelectric-relaxor (FE-R) in the region (1-2x) = 0.08-0.40, and then to the properties of dipole glass with weak correlations in the region (1-2x) > 0.40. It was found that the samples with x = 0.434 and 0.446 below Tc = 414 and 445 K spontaneously pass to the FE state. In the samples with x = 0.42 the application of an electric field of 2.0 kV/ cm induces a transition from FE-R to FE state with Tc = 350 K, which remains after the field is removed

STRUСTURE AND PROPERTIES OF CERAMIC RELAXOR FERROELECTICS OF THE SYSTEM BiScO3 - PbTiO3 WITH MnO2 ADDITIVES IN THE FIELD OF THE MORPHOTROPIC TRANSITION

X-ray diffraction analysis by Rietveld method was carried out for ceramic samples of the system (1-x)BiScO3·xPbTiO3·yMnO2, х=0.63, and y=0.0017 and 0.0118. It was shown that they consist of two phases: tetragonal phase (space group P4mm) and monoclinic phase (space group Cm). The temperature dependencies ε(T) и tgδ(T) were obtained for samples y = 0 - 0.0177 at the frequencies 0.1 - 200 kHz. The samples are ferroelectric with Tc 685-690 K when y ≤ 0.002. With increasing content of MnO2 samples acquire the properties characteristic of ferroelectrics-relaxors. The position of the maximum of dielectric permittivity shifts depending on frequency of measuring field

Development of novel multiferroic composites based on BaTiO3 and hexagonal ferrites

New multiferroic composite ceramics with the general formula (x)Ba(Sr)Fe12O19-(l-x)BaTiO3 (x=O. 1, 0.5) were synthesized via a simple solid-state reaction technique. Crystal structure analysis performed for such materials revealed the presence of two crystalline phases pertinent to the initi2l composite components. X-ray diffraction (XRD), scanning electron microscopy (SEM) nd atomic force microscopy (AFM) were used to assess the crystallinity, microstructure, and local magnetoelectric interactions between ferroelectric and ferromagnetic grains. Magnetic measurements revealed that the saturation magnetization is proportional to the volume fraction of ferrite phase. Dielectric studies demonstrated strong frequency relaxation due to space charge polarization and high conductivity loss making macroscopic magnetoelectric measurements difficult. Novel nanoscale magnetoelectric effect observed by AFM is discussed. © 2009 Materials Research Society