4,901 research outputs found
Magnetic and electric phase control in epitaxial EuTiO from first principles
We propose a design strategy - based on the coupling of spins, optical
phonons, and strain - for systems in which magnetic (electric) phase control
can be achieved by an applied electric (magnetic) field. Using first-principles
density-functional theory calculations, we present a realization of this
strategy for the magnetic perovskite EuTiO.Comment: Significantly revised for clarit
Ferroelectricity in the Dion-Jacobson CsBiNbO from first principles
We have studied ferroelectricity in Dion-Jacobson CsBiNbO from first
principles. Using group-theoretical analysis and first-principles density
functional calculations of the total energy and phonons, we perform a
systematic study of the energy surface around a paraelectric prototypic phase.
Our results suggest that CsBiNbO is a ferroelectric with a polarization
of P=40C cm. We propose further experiments to clarify this
point
Theory of polarization enhancement in epitaxial BaTiO/SrTiO superlattices
The spontaneous polarization of epitaxial BaTiO/SrTiO superlattices
is studied as a function of composition using first-principles density
functional theory within the local density approximation. With the in-plane
lattice parameter fixed to that of bulk SrTiO, the computed superlattice
polarization is enhanced above that of bulk BaTiO for superlattices with
BaTiO fraction larger than 40%. In contrast to their bulk paraelectric
character, the SrTiO layers are found to be {\it tetragonal and polar},
possessing nearly the same polarization as the BaTiO layers. General
electrostatic arguments elucidate the origin of the polarization in the
SrTiO layers, with important implications for other ferroelectric
nanostructures.Comment: 4 pages, 2 Figures, 1 Tabl
Physics of thin-film ferroelectric oxides
This review covers the important advances in recent years in the physics of
thin film ferroelectric oxides, the strongest emphasis being on those aspects
particular to ferroelectrics in thin film form. We introduce the current state
of development in the application of ferroelectric thin films for electronic
devices and discuss the physics relevant for the performance and failure of
these devices. Following this we cover the enormous progress that has been made
in the first principles computational approach to understanding ferroelectrics.
We then discuss in detail the important role that strain plays in determining
the properties of epitaxial thin ferroelectric films. Finally, we look at the
emerging possibilities for nanoscale ferroelectrics, with particular emphasis
on ferroelectrics in non conventional nanoscale geometries.Comment: This is an invited review for Reviews of Modern Physics. We welcome
feedback and will endeavour to incorporate comments received promptly into
the final versio
Epitaxial-strain-induced multiferroicity in SrMnO from first principles
First-principles density-functional calculations reveal a large spin-phonon
coupling in cubic SrMnO, with ferromagnetic ordering producing a polar
instability. Through combination of this coupling with the strain-polarization
coupling characteristic of perovskites, the bulk antiferromagnetic paraelectric
ground state of SrMnO is shown to be driven to a previously unreported
multiferroic ferroelectric-ferromagnetic state by increasing epitaxial strain,
both tensile and compressive. This state has a computed polarization and
estimated Curie temperature above 54 C/cm and 92 K. Large mixed
magnetic-electric-elastic responses are predicted in the vicinity of the phase
boundaries.Comment: 5 pages, 2 figures, 1 tabl
Magnetic-induced phonon anisotropy in ZnCrO from first principles
We have studied the influence of magnetic order on the optical phonons of the
geometrically frustrated spinel ZnCrO from first-principles. By mapping
the first-principles phonon calculations onto a Heisenberg-like model, we
developed a method to calculate exchange derivatives and subsequently the
spin-phonon couping parameter from first-principles. All calculations were
performed within LSDA+U
Coexistence of antiferrodistortive and ferroelectric distortions at the PbTiO (001) surface
The c(22) reconstruction of (001) PbTiO surfaces is studied by
means of first principles calculations for paraelectric (non-polar) and
ferroelectric ([001] polarized) films. Analysis of the atomic displacements in
the near-surface region shows how the surface modifies the antiferrodistortive
(AFD) instability and its interaction with ferroelectric (FE) distortions. The
effect of the surface is found to be termination dependent. The AFD instability
is suppressed at the TiO termination while it is strongly enhanced,
relative to the bulk, at the PbO termination resulting in a c(2x2) surface
reconstruction which is in excellent agreement with experiments. We find that,
in contrast to bulk PbTiO, in-plane ferroelectricity at the PbO termination
does not suppress the AFD instability. The AFD and the in-plane FE distortions
are instead concurrently enhanced at the PbO termination. This leads to a novel
surface phase with coexisting FE and AFD distortions which is not found in
PbTiO bulk
Strain-induced ferroelectricity in CaTiO from first principles
First principles calculations are used to investigate the effects of
epitaxial strain on the structure of the perovskite oxide CaTiO, with
particular focus on the stabilization of a ferroelectric phase related to a
polar instability hidden in the orthorhombic equilibrium bulk structure
but found in previous first-principles studies of the ideal cubic perovskite
high-symmetry reference structure. At 1.5% strain, we find an epitaxial
orientation transition between the - phase, favored for compressive
strains, and the - phase. For larger tensile strains, a polar
instability develops in the - phase and an epitaxial-strain-induced
ferroelectric phase is obtained with polarization along a direction
with respect to the primitive perovskite lattice vectors of the square
substrate.Comment: 4 pages, 2 figure
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