18 research outputs found
Infračervená spektroskopie multiferoik
Infračervená spektroskopie multiferoik Autor:Veronica Goian Ústav: Oddělení dielektrik, Fyzikální ústav AV ČR v.v.i, Na Slovance 2, 182 21, Praha 8 Abstrakt: Pomocí infračervené spektroskopie jsme studovali řadu multiferoických a magnetoelektrických látek. Náš výzkum byl často kombinován radiofrekvečními, mikrovlnnými, teraherzovými, ramanovskými a strukturními měřeními mých kolegů, jakož i magnetickými, a elastickými studiemi, na kterých jsem se podílela. Naším hlavním cílem bylo komplexní studium kvantově- paraelektrického antiferomagnetika EuTiO3 ve formě krystalů, keramik i tenkých vrstev. V objemových vzorcích EuTiO3 jsme objevili u 300 K antiferodistortivní přechod z kubické mPm3 do tetragonální I4/mcm struktury. Nízkoteplotní dielektrické vlastnosti v EuTiO3 jsme vysvětlili anomálním teplotním chováním polárních fononů. Velký a anizotropní magnetoelektrický jev, který jsme našli v EuTiO3, jsme objasnili a experimentálně potvrdili pozorováním ladění fononových frekvencí vnějším magnetickým polem. Naše studia tahově napnutých vrstev EuTiO3 odhalila u 250 K posuvný ferroelektrický fázový přechod. Naši američtí kolegové objevili pod 4.2 K feromagnetické uspořádání ve stejných tenkých vrstvách. Tím jsme experimentálně potvrdili nedávno teoreticky předpovězenou novou možnost přípravy silných...Infrared Spectroscopy of Multiferroics Author: Veronica Goian Institute: Department of Dielectrics, Institute of Physics of the Academy of Sciences, Na Slovance 2, 182 21 Prague 8 Abstract: We have investigated numerous multiferroic and magnetoelectric materials mainly using infrared (IR) spectroscopy. Nevertheless, the studies were frequently combined with radio-frequency, microwave, THz, Raman and structural measurements provided by our colleagues, as well as by magnetic and elastic investigations, where we participated. Our main aim was the complex study of quantum-paraelectric antiferromagnet EuTiO3 in the form of crystals, ceramics and thin films. Near 300 K we have discovered an antiferrodistorive phase transition from cubic mPm3 to tetragonal I4/mcm structure in bulk EuTiO3 and explained its low-frequency dielectric properties by anomalous polar phonon behavior. Large and anisotropic magnetodielectric effect, which we found in EuTiO3, was successfully explained and experimentally confirmed by observation of tuning of phonon frequency with magnetic field. Our IR studies of tensile strained EuTiO3 thin films revealed a displacive ferroelectric phase transition near 250 K. Our American colleagues revealed the ferromagnetic order below 4.2 K in the same strained EuTiO3 thin film. In such way we have...Matematicko-fyzikální fakultaFaculty of Mathematics and Physic
Magnetic and dielectric properties of multiferroic Eu0.5Ba0.25Sr0.25TiO3 ceramics
Dielectric and magnetic properties of Eu0.5Ba0.25Sr0.25TiO3 are investigated
between 10 K and 300 K in the frequency range from 10 Hz to 100 THz. A peak in
permittivity revealed near 130 K and observed ferroelectric hysteresis loops
prove the ferroelectric order below thistemperature. The peak in permittivity
is given mainly by softening of the lowest frequency polar phonon (soft mode
revealed in THz and IR spectra) that demonstrates displacive character of the
phase transition. Room-temperature X-ray diffraction analysis reveals cubic
structure, but the IR reflectivity spectra give evidence of a lower crystal
structure, presumably tetragonal I4/mcm with tilted oxygen octahedra as it has
been observed in EuTiO3. The magnetic measurements show that the
antiferromagnetic order occurs below 1.8 K. Eu0.5Ba0.25Sr0.25TiO3 has three
times lower coercive field than Eu0.5Ba0.5TiO3, therefore we propose this
system for measurements of electric dipole moment of electron.Comment: Phase Transitions, in pres
Possible coupling between magnons and phonons in multiferroic CaMn7O12
Spin and lattice dynamics of CaMn7O12 ceramics were investigated using
infrared, THz and inelastic neutron scattering (INS) spectroscopies in the
temperature range 2 to 590 K, and, at low temperatures, in applied magnetic
fields of up to 12 T. On cooling, we observed phonon splitting accompanying the
structural phase transition at Tc = 450K as well as the onset of the
incommensurately modulated structure at 250 K. In the two antiferromagnetic
phases below T_N1 = 90K and T_N2 = 48 K, several infrared-active excitations
emerge in the meV range; their frequencies correspond to the maxima in the
magnon density of states obtained by INS. At the magnetic phase transitions,
these modes display strong anomalies and for some of them, a transfer of
dielectric strength from the higher-frequency phonons is observed. We propose
that these modes are electromagnons. Remarkably, at least two of these modes
remain active also in the paramagnetic phase; for this reason, we call them
paraelectromagnons. In accordance with this observation, quasielastic neutron
scattering revealed short-range magnetic correlations persisting within
temperatures up to 500K above T_N1
Infrared Spectroscopy of Multiferroics
Infrared Spectroscopy of Multiferroics Author: Veronica Goian Institute: Department of Dielectrics, Institute of Physics of the Academy of Sciences, Na Slovance 2, 182 21 Prague 8 Abstract: We have investigated numerous multiferroic and magnetoelectric materials mainly using infrared (IR) spectroscopy. Nevertheless, the studies were frequently combined with radio-frequency, microwave, THz, Raman and structural measurements provided by our colleagues, as well as by magnetic and elastic investigations, where we participated. Our main aim was the complex study of quantum-paraelectric antiferromagnet EuTiO3 in the form of crystals, ceramics and thin films. Near 300 K we have discovered an antiferrodistorive phase transition from cubic mPm3 to tetragonal I4/mcm structure in bulk EuTiO3 and explained its low-frequency dielectric properties by anomalous polar phonon behavior. Large and anisotropic magnetodielectric effect, which we found in EuTiO3, was successfully explained and experimentally confirmed by observation of tuning of phonon frequency with magnetic field. Our IR studies of tensile strained EuTiO3 thin films revealed a displacive ferroelectric phase transition near 250 K. Our American colleagues revealed the ferromagnetic order below 4.2 K in the same strained EuTiO3 thin film. In such way we have..
Infrared Spectroscopy of Multiferroics
Infrared Spectroscopy of Multiferroics Author: Veronica Goian Institute: Department of Dielectrics, Institute of Physics of the Academy of Sciences, Na Slovance 2, 182 21 Prague 8 Abstract: We have investigated numerous multiferroic and magnetoelectric materials mainly using infrared (IR) spectroscopy. Nevertheless, the studies were frequently combined with radio-frequency, microwave, THz, Raman and structural measurements provided by our colleagues, as well as by magnetic and elastic investigations, where we participated. Our main aim was the complex study of quantum-paraelectric antiferromagnet EuTiO3 in the form of crystals, ceramics and thin films. Near 300 K we have discovered an antiferrodistorive phase transition from cubic mPm3 to tetragonal I4/mcm structure in bulk EuTiO3 and explained its low-frequency dielectric properties by anomalous polar phonon behavior. Large and anisotropic magnetodielectric effect, which we found in EuTiO3, was successfully explained and experimentally confirmed by observation of tuning of phonon frequency with magnetic field. Our IR studies of tensile strained EuTiO3 thin films revealed a displacive ferroelectric phase transition near 250 K. Our American colleagues revealed the ferromagnetic order below 4.2 K in the same strained EuTiO3 thin film. In such way we have..