180 research outputs found
Weak ferromagnetism and internal magnetoelectric effect in LiFePO
The magnetic, thermodynamic, and pyroelectric properties of LiFePO
single crystals are investigated with emphasis on the magnetoelectric
interaction of the electrical polarization with the magnetic order parameter.
The magnetic order below T 27 K is found to be a canted
antiferromagnet with a weak ferromagnetic component along the axis. A sharp
peak of the pyroelectric current at T proves the strong internal
magnetoelectric interaction resulting in a sizable polarization decrease at the
onset of magnetic order. The magnetoelectric effect in external magnetic fields
combines a linear and a quadratic field dependence below T. Thermal
expansion data show a large uniaxial magnetoelastic response and prove the
existence of strong spin lattice coupling. LiFePO is a polar compound
with a strong interaction of the magnetic order parameter with the electric
polarization and the lattice.Comment: 8 pages, 9 figures, to be published in Phys. Rev.
Instability in magnetic materials with dynamical axion field
It has been pointed out that the axion electrodynamics exhibits instability
in the presence of a background electric field. We show that the instability
leads to a complete screening of an applied electric field above a certain
critical value and the excess energy is converted into a magnetic field. We
clarify the physical origin of the screening effect and discuss its possible
experimental realization in magnetic materials where magnetic fluctuations play
the role of the dynamical axion field.Comment: 5 pages, 2 figures; v2: minor editin
Dynamical magnetoelectric effects in multiferroic oxides
Multiferroics with coexistent ferroelectric and magnetic orders can provide
an interesting laboratory to test unprecedented magnetoelectric responses and
their possible applications. One such example is the dynamical and/or resonant
coupling between magnetic and electric dipoles in a solid. As the examples of
such dynamical magnetoelectric effects, (1) the multiferroic domain wall
dynamics and (2) the electric-dipole active magnetic responses are discussed
with the overview of recent experimental observations.Comment: 15 pages including 6 figures; Accepted for publication in Phil.
Trans. A Roy. Soc. (Special issue, Spin on Electronics
Temperature-Dependent Magnetoelectric Effect from First Principles
We show that nonrelativistic exchange interactions and spin fluctuations can give rise to a linear magnetoelectric effect in collinear antiferromagnets at elevated temperatures that can exceed relativistic magnetoelectric responses by more than 1 order of magnitude. We show how symmetry arguments, ab initio methods, and Monte Carlo simulations can be combined to calculate temperature-dependent magnetoelectric susceptibilities entirely from first principles. The application of our method to Cr2O3 gives quantitative agreement with experiment.
Magnetic-field-induced switching between ferroelectric phases in orthorhombic-distortion-controlled MnO
We have investigated the dielectric and magnetic properties of
EuYMnO the presence of the 4 magnetic
moments of the rare earth ions, and have found two ferroelectric phases with
polarization along the and axes in a zero magnetic field. A magnetic
field induced switching from one to the other ferroelectric phase took plase in
which the direction of ferroelectric polarization changed from the a axis to
the c axis by the application of magnetic fields parallel to the a axis. In
contrast to the case of TbMnO, in which the 4 moments of Tb
ions play an important role in such a ferroelectric phase switching, the
magnetic-field-induced switching between ferroelectric phases in
EuYMnO does not originate from the magnetic
transition of the rare-earth 4 moments, but from that of the Mn 3 spins.Comment: 8 pages, 3 figures, RevTeX4, Proceedings of MMM 2005, to appear in J.
Appl. Phy
First-principles approach to lattice-mediated magnetoelectric effects
We present a first-principles scheme for the computation of the
magnetoelectric response of magnetic insulators. The method focuses on the
lattice-mediated part of the magnetic response to an electric field, which we
argue can be expected to be the dominant contribution in materials displaying a
strong magnetoelectric coupling. We apply our method to Cr2O3, a relatively
simple and experimentally well studied magnetoelectric compound.Comment: 4 pages with 1 figure embedded. More information at
http://www.icmab.es/dmmis/leem/jorg
Analysis of optical magnetoelectric effect in GaFeO_3
We study the optical absorption spectra in a polar ferrimagnet GaFeO_3. We
consider the E1, E2 and M1 processes on Fe atoms. It is shown that the
magnetoelectric effect on the absorption spectra arises from the E1-M1
interference process through the hybridization between the 4p and 3d states in
the noncentrosymmetry environment of Fe atoms. We perform a microscopic
calculation of the spectra on a cluster model of FeO_6 consisting of an
octahedron of O atoms and an Fe atom displaced from the center with reasonable
values for Coulomb interaction and hybridization. We obtain the magnetoelectric
spectra, which depend on the direction of magnetization, as a function of
photon energy in the optical region 1.0-2.5 eV, in agreement with the
experiment.Comment: 18 pages, 5 figure
Neel state of antiferromagnet as a result of a local measurement in the distributed quantum system
Single-site measurement in a distributed macroscopic antiferromagnet is
considered; we show that it can create antiferromagnetic sublattices at
macroscopic scale. We demonstrate that the result of measurement depends on the
symmetry of the ground state: for the easy-axis case the Neel state is formed,
while for the easy-plane case unusual ``fan'' sublattices appear with unbroken
rotational symmetry, and a decoherence wave is generated. For the latter case,
a macroscopically large number of measurements is needed to pin down the
orientation of the sublattices, in spite of the high degeneracy of the ground
state. We note that the type of the final state and the appearance of the
decoherence wave are governed by the degree of entanglement of spins in the
system.Comment: 4 REVTeX pages, 1 figure in PostScrip
Relativistic nature of a magnetoelectric modulus of Cr_2O_3-crystals: a new 4-dimensional pseudoscalar and its measurement
Earlier, the magnetoelectric effect of chromium sesquioxide Cr_2O_3 has been
determined experimentally as a function of temperature. One measures the
electric field-induced magnetization on Cr_2O_3 crystals or the magnetic
field-induced polarization. From the magnetoelectric moduli of Cr_2O_3 we
extract a 4-dimensional relativistic invariant pseudoscalar
. It is temperature dependent and of the order of
10^{-4}/Z_0, with Z_0 as vacuum impedance. We show that the new pseudoscalar is
odd under parity transformation and odd under time inversion. Moreover,
is for Cr_2O_3 what Tellegen's gyrator is for two port
theory, the axion field for axion electrodynamics, and the PEMC (perfect
electromagnetic conductor) for electrical engineering.Comment: Revtex, 36 pages, 9 figures (submitted in low resolution, better
quality figures are available from the authors
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