1,552 research outputs found
Mechanisms and origin of multiferroicity
Motivated by the potential applications of their intrinsic cross-coupling
properties, the interest in multiferroic materials has constantly increased
recently, leading to significant experimental and theoretical advancements.
From the theoretical point of view, recent progresses have allowed to identify
different mechanisms responsible for the appearence of ferroelectric
polarization coexisting with -- and coupled to -- magnetic properties. This
chapter aims at reviewing the fundamental mechanisms devised so far, mainly in
transition-metal oxides, which lie at the origin of multiferroicity
Spontaneous skyrmionic lattice from anisotropic symmetric exchange in a Ni-halide monolayer
Topological spin structures, such as magnetic skyrmions, hold great promises
for data storage applications, thanks to their inherent stability. In most
cases, skyrmions are stabilized by magnetic fields in non-centrosymmetric
systems displaying the chiral Dzyaloshinskii-Moriya exchange interaction, while
spontaneous skyrmion lattices have been reported in centrosymmetric itinerant
magnets with long-range interactions. Here, a spontaneous anti-biskyrmion
lattice with unique topology and chirality is predicted in the monolayer of a
semiconducting and centrosymmetric metal halide, NiI. Our first-principles
and Monte Carlo simulations reveal that the anisotropies of the short-range
symmetric exchange, when combined with magnetic frustration, can lead to an
emergent chiral interaction that is responsible for the predicted topological
spin structures. The proposed mechanism finds a prototypical manifestation in
two-dimensional magnets, thus broadening the class of materials that can host
spontaneous skyrmionic states.Comment: submitte
Ferroelectricity due to orbital ordering in E-type undoped rare-earth manganites
Aiming at understanding the origin of the electronic contribution to
ferroelectric polarization in undoped manganites, we evaluate the Berry phase
of orbital-polarizable Bloch electrons as an orbital ordering (OO) establishes
in the background of an antiferromagnetic E-type configuration. The onset of OO
is tuned by the Jahn-Teller (JT) interaction in a tight-binding model for
interacting electrons moving along zigzag chains. A finite polarization is
found as soon as the JT coupling is strong enough to induce OO, supporting the
large electronic contribution predicted from first principles.Comment: 4 pages, 2 figures, figure and text substantially improved. Title
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Theoretical investigation of magnetoelectric effects in Ba2CoGe2O7
A joint theoretical approach, combining macroscopic symmetry analysis with
microscopic methods (density functional theory and model cluster Hamiltonian),
is employed to shed light on magnetoelectricity in Ba2CoGe2O7. We show that the
recently reported experimental trend of polarization guided by magnetic field
can be predicted on the basis of phenomenological Landau theory. From the
microscopic side, Ba2CoGe2O7 emerges as a prototype of a class of
magnetoelectrics, where the cross coupling between magnetic and dipolar degrees
of freedom needs, as main ingredients, the on-site spin-orbit coupling and the
spin-dependent O p - Co d hybridization, along with structural constraints
related to the noncentrosymmetric structural symmetry and the peculiar
configuration of CoO4 tetrahedrons.Comment: 5 pages, 4 figures, submitted for publicatio
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