212 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.
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
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
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
Solid State Systems for Electron Electric Dipole Moment and other Fundamental Measurements
In 1968, F.L. Shapiro published the suggestion that one could search for an
electron EDM by applying a strong electric field to a substance that has an
unpaired electron spin; at low temperature, the EDM interaction would lead to a
net sample magnetization that can be detected with a SQUID magnetometer. One
experimental EDM search based on this technique was published, and for a number
of reasons including high sample conductivity, high operating temperature, and
limited SQUID technology, the result was not particularly sensitive compared to
other experiments in the late 1970's.
Advances in SQUID and conventional magnetometery had led us to reconsider
this type of experiment, which can be extended to searches and tests other than
EDMs (e.g., test of Lorentz invariance). In addition, the complementary
measurement of an EDM-induced sample electric polarization due to application
of a magnetic field to a paramagnetic sample might be effective using modern
ultrasensitive charge measurement techniques. A possible paramagnetic material
is Gd-substituted YIG which has very low conductivity and a net enhancement
(atomic enhancement times crystal screening) of order unity. Use of a
reasonable volume (100's of cc) sample of this material at 50 mK and 10 kV/cm
might yield an electron EDM sensitivity of e cm or better, a factor
of improvement over current experimental limits.Comment: 6 pages. Prepared for ITAMP workshop on fundamental physics that was
to be held Sept 20-22 2001 in Cambride, MA, but was canceled due to terrorist
attack on U.S New version incorporates a number of small changes, most
notably the scaling of the sensitivity of the Faraday magnetometer with
linewidth is now treated in a saner fashion. The possibility of operating at
an even lower temperarture, say 10 microkelvin, is also discusse
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
Theoretical prediction of multiferroicity in double perovskite YNiMnO
We put forward double perovskites of the RNiMnO family (with a
rare-earth atom) as a new class of multiferroics on the basis of {\it ab
initio} density functional calculations. We show that changing from La to Y
drives the ground-state from ferromagnetic to antiferromagnetic with
spin patterns. This E-type ordering
breaks inversion symmetry and generates a ferroelectric polarization of few
. By analyzing a model Hamiltonian we understand the microscopic
origin of this transition and show that an external electric field can be used
to tune the transition, thus allowing electrical control of the magnetization.Comment: 4 pages, 3 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
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