296 research outputs found
Effect of magnetic field and temperature on the ferroelectric loop in MnWO4
The ferroelectric properties of MnWO4 single crystal have been investigated.
Despite a relatively low remanent polarization, we show that the sample is
ferroelectric. The shape of the ferroelectric loop of MnWO4 strongly depends on
magnetic field and temperature. While its dependence does not directly
correlate with the magnetocapacitance effect before the paraelectric
transition, the effect of magnetic field on the ferroelectric polarization loop
supports magnetoelectric coupling.Comment: 3 pages, 4 figures, first report on ferroelectric loop in MnWO
Magnetophononics: ultrafast spin control through the lattice
Using a combination of first-principles and magnetization-dynamics
calculations, we study the effect of the intense optical excitation of phonons
on the magnetic behavior in insulating magnetic materials. Taking the
prototypical magnetoelectric \CrO\ as our model system, we show that excitation
of a polar mode at 17 THz causes a pronounced modification of the magnetic
exchange interactions through a change in the average Cr-Cr distance. In
particular, the quasi-static deformation induced by nonlinear phononic coupling
yields a structure with a modified magnetic state, which persists for the
duration of the phonon excitation. In addition, our time-dependent
magnetization dynamics computations show that systematic modulation of the
magnetic exchange interaction by the phonon excitation modifies the
magnetization dynamics. This temporal modulation of the magnetic exchange
interaction strengths using phonons provides a new route to creating
non-equilibrium magnetic states and suggests new avenues for fast manipulation
of spin arrangements and dynamics.Comment: 11 pages with 7 figure
First-principles study of ferroelectric domain walls in multiferroic bismuth ferrite
We present a first-principles density functional study of the structural,
electronic and magnetic properties of the ferroelectric domain walls in
multiferroic BiFeO3. We find that domain walls in which the rotations of the
oxygen octahedra do not change their phase when the polarization reorients are
the most favorable, and of these the 109 degree domain wall centered around the
BiO plane has the lowest energy. The 109 degree and 180 degree walls have a
significant change in the component of their polarization perpendicular to the
wall; the corresponding step in the electrostatic potential is consistent with
a recent report of electrical conductivity at the domain walls. Finally, we
show that changes in the Fe-O-Fe bond angles at the domain walls cause changes
in the canting of the Fe magnetic moments which can enhance the local
magnetization at the domain walls.Comment: 9 pages, 20 figure
Ferrodistortive instability at the (001) surface of half-metallic manganites
We present the structure of the fully relaxed (001) surface of the
half-metallic manganite La0.7Sr0.3MnO3, calculated using density functional
theory within the generalized gradient approximation (GGA). Two relevant
ferroelastic order parameters are identified and characterized: The tilting of
the oxygen octahedra, which is present in the bulk phase, oscillates and
decreases towards the surface, and an additional ferrodistortive Mn
off-centering, triggered by the surface, decays monotonically into the bulk.
The narrow d-like energy band that is characteristic of unrelaxed manganite
surfaces is shifted down in energy by these structural distortions, retaining
its uppermost layer localization. The magnitude of the zero-temperature
magnetization is unchanged from its bulk value, but the effective spin-spin
interactions are reduced at the surface.Comment: 4 pages, 2 figure
Coupling between magnetic ordering and structural instabilities in perovskite biferroics: A first-principles study
We use first-principles density functional theory-based calculations to
investigate structural instabilities in the high symmetry cubic perovskite
structure of rare-earth (R La, Y, Lu) and Bi-based biferroic chromites,
focusing on and point phonons of states with para-, ferro-, and
antiferromagnetic ordering. We find that (a) the structure with G-type
antiferromagnetic ordering is most stable, (b) the most dominant structural
instabilities in these oxides are the ones associated with rotations of oxygen
octahedra, and (c) structural instabilities involving changes in Cr-O-Cr bond
angle depend sensitively on the changes in magnetic ordering. The dependence of
structural instabilities on magnetic ordering can be understood in terms of how
super-exchange interactions depend on the Cr-O-Cr bond angles and Cr-O bond
lengths. We demonstrate how adequate buckling of Cr-O-Cr chains can favour
ferromagnetism. Born effective charges (BEC) calculated using the Berry phase
expression are found to be anomalously large for the A-cations, indicating
their chemical relevance to ferroelectric distortions.Comment: 8 pages, 13 figure
Influence of strain and oxygen vacancies on the magnetoelectric properties of multiferroic bismuth ferrite
The dependencies on strain and oxygen vacancies of the ferroelectric
polarization and the weak ferromagnetic magnetization in the multiferroic
material bismuth ferrite, BiFeO_3, are investigated using first principles
density functional theory calculations. The electric polarization is found to
be rather independent of strain, in striking contrast to most conventional
perovskite ferroelectrics. It is also not significantly affected by oxygen
vacancies, or by the combined presence of strain and oxygen vacancies. The
magnetization is also unaffected by strain, however the incorporation of oxygen
vacancies can alter the magnetization slightly, and also leads to the formation
of Fe^{2+}. These results are discussed in light of recent experiments on
epitaxial films of BiFeO_3 which reported a strong thickness dependence of both
magnetization and polarization.Comment: 9 pages, 3 figure
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