258 research outputs found
Spin-glass state and long-range magnetic order in Pb(Fe1/2Nb1/2)O3
We have investigated the magnetic ground-state of the multiferroic relaxor
ferroelectric \pfn with SR spectroscopy and neutron scattering. We find
that a transition to a partially disordered phase occurs below T=20 K that
coexists with long-range antiferromagnetic ordering. The disordered phase
resembles a spin-glass. No clustering of magnetic ions could be evidenced by
SR so that the coexistence appears homogeneous in the sample
Development of Ferroelectric Order in Relaxor (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3
The microstructure and phase transition in relaxor ferroelectric
Pb(Mg1/3Nb2/3)O3 (PMN) and its solid solution with PbTiO3 (PT), PMN-xPT, remain
to be one of the most puzzling issues of solid state science. In the present
work we have investigated the evolution of the phase symmetry in PMN-xPT
ceramics as a function of temperature (20 K < T < 500 K) and composition (0 <=
x <= 0.15) by means of high-resolution synchrotron x-ray diffraction.
Structural analysis based on the experimental data reveals that the
substitution of Ti^4+ for the complex B-site (Mg1/3Nb2/3)^4+ ions results in
the development of a clean rhombohedral phase at a PT-concentration as low as
5%. The results provide some new insight into the development of the
ferroelectric order in PMN-PT, which has been discussed in light of the
kinetics of polar nanoregions and the physical models of the relaxor
ferroelectrics to illustrate the structural evolution from a relaxor to a
ferroelectric state.Comment: Revised version with updated references; 9 pages, 4 figures embedde
A muon-spin relaxation study of BiMnO3
We present the results of muon-spin relaxation measurements on ferromagnetic
BiMnO3. Below T_C=98.0(1) K oscillations in the time-dependence of the muon
polarization are observed, characteristic of a quasistatic magnetic field at a
single muon site, allowing us to probe the critical behaviour associated with
the magnetic phase transition. We are able to suggest candidate muon sites on
the basis of dipole field calculations. Close to T_C, fluctuations of the Mn^3+
moments are characteristic of critical behaviour while there is a sharp
crossover to a region of fast dynamic fluctuations at higher temperatures.Comment: 10 pages, 4 figure
Spatially Resolved Mapping of Local Polarization Dynamics in an Ergodic Phase of Ferroelectric Relaxor
Spatial variability of polarization relaxation kinetics in relaxor
ferroelectric 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 is studied using time-resolved
Piezoresponse Force Microscopy. Local relaxation attributed to the
reorientation of polar nanoregions is shown to follow stretched exponential
dependence, exp(-(t/tau)^beta), with beta~~0.4, much larger than the
macroscopic value determined from dielectric spectra (beta~~0.09). The spatial
inhomogeneity of relaxation time distributions with the presence of 100-200 nm
"fast" and "slow" regions is observed. The results are analyzed to map the
Vogel-Fulcher temperatures on the nanoscale.Comment: 23 pages, 4 figures, supplementary materials attached; to be
submitted to Phys. Rev. Let
Conversion of radar signal when seminatural modeling of multipath propagation
The report examines the features of transformation of the emitted signal in hardware in the loop simulations for radar systems when simulating the reflection from extended surfaces. The methods used to implement instrument testing radio altimeters with chirp modulation frequency and other radar systems with continuous or long-emitted signal with the ability to change parameters of all signals in real-time.В докладе рассматриваются особенности преобразования излученного сигнала в аппаратуре полунатурного моделирования для радиолокационных систем при имитации отражения от протяженных поверхностей. Приведенные методы используются для реализации аппаратуры испытаний радиовысотомеров с ЛЧМ-модуляцией частоты и других радиолокационных систем с непрерывным или длительно излучаемым сигналом с возможностью изменения параметров всех сигналов в режиме реального времени
Magnetocaloric effect in the high-temperature antiferromagnet YbCoC2
The magnetic - phase diagram and magnetocaloric effect in the recently
discovered high-temperature heavy-fermion compound YbCoC have been studied.
With the increase in the external magnetic field YbCoC experiences the
metamagnetic transition and then transition to the ferromagnetic state. The
dependencies of magnetic entropy change - have segments with
positive and negative magnetocaloric effects for ~T. For
~T magnetocaloric effect becomes positive with a maximum value of
- is 4.1 J / kg K and a refrigerant capacity is 56.6 J / kg
Block-modular technology training in the discipline of «Electromagnetic fields and waves» using learning management system «Moodle»
The results of the development and implementation of block-modular technology in the learning process of students using a learning management system "MOODLE" in the example, the academic discipline of "Еlectromagnetic fields and waves".Изложены результаты разработки и внедрения блочно-модульной технологии в процесс обучения студентов с использованием системы управления обучением «МOODLE» на примере учебной дисциплины «Электромагнитные поля и волны»
Phonon and magnon scattering of antiferromagnetic Bi2Fe4O9
The phonon structure of antiferromagnetic Bi2Fe4O9 (space group Pbnm No. 55, TN≈240 K) was studied theoretically by calculations of lattice dynamics and experimentally between 10 and 300 K by polarized Raman spectroscopy. Most of the 12Ag+12B1g+9B2g+9B3g Raman modes were unambiguously identified. Strong second-order scattering was observed for ab-plane-confined incident and scattered light polarizations. In addition to the phonon-scattering, broad Raman bands with typical characteristics of magnon scattering appear below TN. The magnon bands are analyzed on the basis of magnetic structure of Bi2Fe4O9 and attributed to two- magnon excitations
Chemically engineered multiferroic Morphotropic Phase Boundary in BiFeO3-based single phase multiferroics
Soft Phonon Anomalies in the Relaxor Ferroelectric Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3
Neutron inelastic scattering measurements of the polar TO phonon mode
dispersion in the cubic relaxor Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3 at 500K reveal
anomalous behavior in which the optic branch appears to drop precipitously into
the acoustic branch at a finite value of the momentum transfer q=0.2 inverse
Angstroms, measured from the zone center. We speculate this behavior is the
result of nanometer-sized polar regions in the crystal.Comment: 4 pages, 4 figure
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