34 research outputs found
Incompatible Magnetic Order in Multiferroic Hexagonal DyMnO3
Magnetic order of the manganese and rare-earth lattices according to
different symmetry representations is observed in multiferroic hexagonal (h-)
DyMnO by optical second harmonic generation and neutron diffraction. The
incompatibility reveals that the 3d-4f coupling in the h-MnO system (
= Sc, Y, In, Dy - Lu) is substantially less developed than commonly expected.
As a consequence, magnetoelectric coupling effects in this type of split-order
parameter multiferroic that were previously assigned to a pronounced 3d-4f
coupling have now to be scrutinized with respect to their origin
Second harmonic generation on incommensurate structures: The case of multiferroic MnWO4
A comprehensive analysis of optical second harmonic generation (SHG) on an
incommensurate (IC) magnetically ordered state is presented using multiferroic
MnWO4 as model compound. Two fundamentally different SHG contributions coupling
to the primary IC magnetic order or to secondary commensurate projections of
the IC state, respectively, are distinguished. Whereas the latter can be
described within the formalism of the 122 commensurate magnetic point groups
the former involves a breakdown of the conventional macroscopic symmetry
analysis because of its sensitivity to the lower symmetry of the local
environment in a crystal lattice. Our analysis thus foreshadows the fusion of
the hitherto disjunct fields of nonlinear optics and IC order in
condensed-matter systems
Robust isothermal electric switching of interface magnetization: A route to voltage-controlled spintronics
Roughness-insensitive and electrically controllable magnetization at the
(0001) surface of antiferromagnetic chromia is observed using magnetometry and
spin-resolved photoemission measurements and explained by the interplay of
surface termination and magnetic ordering. Further, this surface in placed in
proximity with a ferromagnetic Co/Pd multilayer film. Exchange coupling across
the interface between chromia and Co/Pd induces an electrically controllable
exchange bias in the Co/Pd film, which enables a reversible isothermal (at room
temperature) shift of the global magnetic hysteresis loop of the Co/Pd film
along the magnetic field axis between negative and positive values. These
results reveal the potential of magnetoelectric chromia for spintronic
applications requiring non-volatile electric control of magnetization.Comment: Single PDF file: 27 pages, 6 figures; version of 12/30/09; submitted
to Nature Material
New features in the phase diagram of TbMnO
The (H,T)-phase diagram of the multiferroic perovskite TbMnO was studied
by high-resolution thermal expansion and magnetostriction measurements. Below K, TbMnO shows
antiferromagnetic order, which changes at K where
simultaneously a spontaneous polarization develops. Sufficiently high
magnetic fields applied along or induce a polarization flop to .
We find that all of these transitions are strongly coupled to the lattice
parameters. Thus, our data allow for a precise determination of the phase
boundaries and also yield information about their uniaxial pressure
dependencies. The strongly hysteretic phase boundary to the ferroelectric phase
with is derived in detail. Contrary to previous reports, we find that
even in high magnetic fields there are no direct transitions from this phase to
the paraelectric phase. We also determine the various phase boundaries in the
low-temperature region related to complex reordering transitions of the Tb
moments.Comment: 17 pages including 9 figure
Relaxor ferroelectricity and colossal magnetocapacitive coupling in ferromagnetic CdCr2S4
Multiferroic materials, which reveal magnetic and electric order, are in the
focus of recent solid state research. Especially the simultaneous occurrence of
ferroelectricity and ferromagnetism, combined with an intimate coupling of
magnetization and polarization via magneto-capacitive effects, could pave the
way for a new generation of electronic devices. Here we present measurements on
a simple cubic spinel with unusual properties: It shows ferromagnetic order and
simultaneously relaxor ferroelectricity, i.e. a ferroelectric cluster state,
reached by a smeared-out phase transition, both with sizable ordering
temperatures and moments. Close to the ferromagnetic ordering temperature the
magneto-capacitive coupling, characterized by a variation of the dielectric
constant in an external magnetic field, reaches colossal values of nearly 500%.
We attribute the relaxor properties to geometric frustration, which is well
known for magnetic moments, but here is found to impede long-range order of the
structural degrees of freedom.Comment: 4 pages, 3 figure
Interconversion of multiferroic domains and domain walls
International audienceAbstract Systems with long-range order like ferromagnetism or ferroelectricity exhibit uniform, yet differently oriented three-dimensional regions called domains that are separated by two-dimensional topological defects termed domain walls. A change of the ordered state across a domain wall can lead to local non-bulk physical properties such as enhanced conductance or the promotion of unusual phases. Although highly desirable, controlled transfer of these properties between the bulk and the spatially confined walls is usually not possible. Here, we demonstrate this crossover by confining multiferroic Dy 0.7 Tb 0.3 FeO 3 domains into multiferroic domain walls at an identified location within a non-multiferroic environment. This process is fully reversible; an applied magnetic or electric field controls the transformation. Aside from expanding the concept of multiferroic order, such interconversion can be key to addressing antiferromagnetic domain structures and topological singularities