224 research outputs found
Magnetic digital flop of ferroelectric domain with fixed spin chirality in a triangular lattice helimagnet
Ferroelectric properties in magnetic fields of varying magnitude and
direction have been investigated for a triangular-lattice helimagnet
CuFe1-xGaxO2 (x=0.035). The magnetoelectric phase diagrams were deduced for
magnetic fields along [001], [110], and [1-10] direction, and the in-plane
magnetic field was found to induce the rearrangement of six possible
multiferroic domains. Upon every 60-degree rotation of in-plane magnetic field
around the c-axis, unique 120-degree flop of electric polarization occurs as a
result of the switch of helical magnetic q-vector. The chirality of spin helix
is always conserved upon the q-flop. The possible origin is discussed in the
light of the stable structure of multiferroic domain wall.Comment: 5 pages, 4 figures. Accepted in Phys. Rev. Let
The Lorenz number in CeCoIn inferred from the thermal and charge Hall currents
The thermal Hall conductivity and Hall conductivity
in CeCoIn are used to determine the Lorenz number at low temperature . This enables the separation of the observed
thermal conductivity into its electronic and non-electronic parts. We uncover
evidence for a charge-neutral, field-dependent thermal conductivity, which we
identify with spin excitations. At low , these excitations dominate the
scattering of charge carriers. We show that suppression of the spin excitations
in high fields leads to a steep enhancement of the electron mean-free-path,
which leads to an interesting scaling relation between the magnetoresistance,
thermal conductivity and .Comment: 6 pages, 7 figures Intro para slightly lengthened. Added 2 new re
Ferroelectricity induced by spin-dependent metal-ligand hybridization in BaCoGeO
We have investigated the variation of induced ferroelectric polarization
under magnetic field with various directions and magnitudes in a staggered
antiferromagnet BaCoGeO. While the ferroelectric polarization
cannot be explained by the well-accepted spin current model nor exchange
striction mechanism, we have shown that it is induced by the spin-dependent
- hybridization between the transition-metal (Co) and ligand (O) via the
spin-orbit interaction. On the basis of the correspondence between the
direction of electric polarization and the magnetic state, we have also
demonstrated the electrical control of the magnetization direction.Comment: 4 pages, 4 figure
Giant directional dichroism of terahertz light in resonance with magnetic excitations of the multiferroic oxide BaCoGeO
We propose that concurrently magnetic and ferroelectric, i.e. multiferroic,
compounds endowed with electrically-active magnetic excitations
(electromagnons) provide a key to produce large directional dichroism for long
wavelengths of light. By exploiting the control of ferroelectric polarization
and magnetization in a multiferroic oxide BaCoGeO, we demonstrate
the realization of such a directional light-switch function at terahertz
frequecies in resonance with the electromagnon absorption. Our results imply
that this hidden potential is present in a broad variety of multiferroics
Anomalous thermopower and Nernst effect in : entropy-current loss in precursor state
The heavy-electron superconductor CeCoIn exhibits a puzzling precursor
state above its superconducting critical temperature at = 2.3 K. The
thermopower and Nernst signal are anomalous. Below 15 K, the entropy current of
the electrons undergoes a steep decrease reaching 0 at .
Concurrently, the off-diagonal thermoelectric current is
enhanced. The delicate sensitivity of the zero-entropy state to field implies
phase coherence over large distances. The prominent anomalies in the
thermoelectric current contrast with the relatively weak effects in the
resistivity and magnetization.Comment: 5 figures, 4 page
Chemical Potential Shift in NdCeCuO: Contrasting Behaviors of the Electron- and Hole-Doped Cuprates
We have studied the chemical potential shift in the electron-doped
superconductor NdCeCuO by precise measurements of
core-level photoemission spectra. The result shows that the chemical potential
monotonously increases with electron doping, quite differently from
LaSrCuO, where the shift is suppressed in the underdoped
region.
If the suppression of the shift in LaSrCuO is attributed
to strong stripe fluctuations, the monotonous increase of the chemical
potential is consistent with the absence of stripe fluctuations in
NdCeCuO. The chemical potential jump between
NdCuO and LaCuO is found to be much smaller than the
optical band gaps.Comment: 4 pages, 5 figure
Universal Scaling Behavior of Anomalous Hall Effect and Anomalous Nernst Effect in Itinerant Ferromagnets
Anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in a variety of
ferromagnetic metals including pure metals, oxides, and chalcogenides, are
studied to obtain unified understandings of their origins. We show a universal
scaling behavior of anomalous Hall conductivity as a function of
longitudinal conductivity over five orders of magnitude, which is
well explained by a recent theory of the AHE taking into account both the
intrinsic and extrinsic contributions. ANE is closely related with AHE and
provides us with further information about the low-temperature electronic state
of itinerant ferromagnets. Temperature dependence of transverse Peltier
coefficient shows an almost similar behavior among various
ferromagnets, and this behavior is in good agreement quantitatively with that
expected from the Mott rule.Comment: 4pages, 4figures, 1tabl
Dynamics of Multiferroic Domain Wall in Spin-Cycloidal Ferroelectric DyMnO
We report the dielectric dispersion of the giant magnetocapacitance (GMC) in
multiferroic DyMnO over a wide frequency range. The GMC is found to be
attributable not to the softened electromagnon but to the electric-field-driven
motion of multiferroic domain wall (DW). In contrast to conventional
ferroelectric DWs, the present multiferroic DW motion holds extremely high
relaxation rate of s even at low temperatures. This
mobile nature as well as the model simulation suggests that the multiferroic DW
is not atomically thin as in ferroelectrics but thick, reflecting its magnetic
origin.Comment: 4 pages, 4 figure
Electric current control of spin helicity in an itinerant helimagnet
Chirality is breaking of mirror symmetry in matter. In the fields of biology
and chemistry, this is particularly important because some of the essential
molecules in life such as amino acids and DNA have chirality. It is a
long-standing mystery how one of the enantiomers was chosen at the beginning
stage of life. The understanding of the emergence of homochirality under some
conditions is indispensable for the study of the origin of life as well as
pharmaceutical science. The chirality is also emergent in magnetic structures.
The longitudinal helical magnetic structure is the chiral object composed of
magnetic moments, in which the ordered direction of the magnetic moment
spatially rotates in the plane perpendicular to the propagation vector (Fig.
1a). Since the sense of rotation, which is denoted as helicity, is reversed by
any mirror operation, it is corresponding to the chirality. Here we show that
the chirality of a longitudinal helical structure can be controlled by the
magnetic field and electric current owing to the spin-transfer torque
irrelevant to the spin-orbit interaction and probed by electrical magnetochiral
effect, which is sensitive to the chiral symmetry breaking, in an itinerant
helimagnet MnP. This phenomenon is distinct from the multiferroicity in
transverse-type insulating helical magnets, in which the helical plane is
parallel to the propagation vector, because the magnetic structure has polar
symmetry not chiral one. While the combination of the magnetic field and
electric current satisfies the symmetrical rule of external stimulus for the
chirality control, the control with them was not reported for any chiral object
previously. The present result may pave a new route to the control of
chiralities originating from magnetic and atomical arrangements.Comment: 14 pages, 7 figure
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