1,075 research outputs found
Substrate coherency-driven octahedral rotations in perovskite oxide films
We perform first-principles density functional calculations to explore the
role of substrate proximity effects on the octahedral rotation patterns in
perovskite oxide superlattices. With cubic perovskite SrFeO as our model
film and tetragonal SrTiO as the substrate, we show that in most cases the
substrate octahedral rotation patterns propagate into the film across the
heterointerface. We also identify elastic boundary conditions for which the
enforced structural coherence induces atomic displacement patterns that are not
found in the bulk phase diagram of either individual constituent. We suggest
that such substrate coherency-induced octahedral texturing of thin film oxides
is a promising approach for tuning the electronic structure of functional oxide
thin films.Comment: 5 pages, 4 figure
BaNiF4: an electric field-switchable weak antiferromagnet
We show that in the antiferromagnetic ferroelectric BaNiF4 the
Dzyaloshinskii-Moriya interaction leads to a small canting of the magnetic
moments, away from the easy axis, resulting in a noncollinear magnetic
structure. The canting corresponds to an additional "weak" antiferromagnetic
order parameter whose orientation is determined by the polar structural
distortion and can be reversed by switching the ferroelectric polarization with
an electric field. Our results point the way to a more general coupling
mechanism between structural distortions and magnetic order parameters in
magnetoelectric multiferroics which can be exploited in the design of electric
field-switchable magnets.Comment: 4 pages, 4 figure
Interplay between strain, defect charge state and functionality in complex oxides
We use first-principles calculations to investigate the interplay between
strain and the charge state of point defect impurities in complex oxides. Our
work is motivated by recent interest in using defects as active elements to
provide novel functionality in coherent epitaxial films. Using oxygen vacancies
as model point defects, and CaMnO and MnO as model materials, we calculate
the changes in internal strain caused by changing the charge state of the
vacancies, and conversely the effect of strain on charge-state stability. Our
results show that the charge state is a degree of freedom that can be used to
control the interaction of defects with strain and hence the concentration and
location of defects in epitaxial films. We propose the use of field-effect
gating to reversibly change the charge state of defects and hence the internal
strain and corresponding strain-induced functionalities.Comment: 4 pages, 4 figure
High-temperature multiferroicity and strong magnetocrystalline anisotropy in 3d-5d double perovskites
Using density functional calculations we explore the properties of
as-yet-unsynthesized ordered double perovskites (O) with
highly polarizable Bi ions on the site. We find that the
BiNiReO and BiMnReO compounds are insulating and exhibit a
robust net magnetization that persists above room temperature. When the
in-plane lattice vectors of the pseudocubic unit cell are constrained to be
orthogonal (for example, by coherent heteroepitaxy), the ground states are
ferroelectric with large polarization and a very large uniaxial
magnetocrystalline anisotropy with easy axis along the ferroelectric
polarization direction. Our results suggest a route to multiferroism and
electrically controlled magnetization orientation at room temperature
Self-interaction correction with Wannier functions
We describe the behavior of the Perdew-Zunger self-interaction-corrected
local density approximation (SIC-LDA) functional when implemented in a
plane-wave pseudopotential formalism with Wannier functions. Prototypical
semiconductors and wide-bandgap oxides show a large overcorrection of the LDA
bandgap. Application to transition-metal oxides and elements with d electrons
is hindered by a serious breaking of the spherical symmetry, which appears even
in a closed shell free atom. Our results indicate that, when all spherical
approximations are lifted, the general applicability of orbital-dependent
potentials is very limited and should be reconsidered in favor of rotationally
invariant functionals.Comment: 10 pages, 5 figure
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