H. Murakawa

Low-magnetic-field control of electric polarization vector in a helimagnet.

The mutual control of the electric and magnetic properties of a solid is currently of great interest because of the possible application for novel electronic devices. We report on the low-magnetic-field (for example, B values of ±30 milliteslas) control of the polarization (P) vector in a hexaferrite, Ba2Mg2Fe12O22, which shows the helimagnetic spin structure with the propagation vector k0 parallel to [001]. The B-induced transverse conical spin structure carries the P vector directing perpendicular to both B and k0, in accord with the recently proposed spin-current model. Then, the oscillating or multidirectionally rotating B produces the cyclic displacement current via the flexible handling of the magnetic cone axis.

Ferroelectricity induced by spin-dependent metal-ligand hybridization in Ba₂CoGe₂O₇.

We have investigated the variation of induced ferroelectric polarization under a magnetic field with various directions and magnitudes in a staggered antiferromagnet Ba₂CoGe₂O₇. While the ferroelectric polarization cannot be explained by the well-accepted spin current model nor the exchange striction mechanism, we have shown that it is induced by the spin-dependent p-d 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.

Enhanced directional dichroism of terahertz light in resonance with magnetic excitations of the multiferroic Ba2CoGe2O 7 oxide compound

We propose that concurrently magnetic and ferroelectric, i.e., multiferroic, compounds endowed with electrically active magnetic excitations (electromagnons) provide a key to producing large directional dichroism for long wavelengths of light. By exploiting the control of ferroelectric polarization and magnetization in a multiferroic oxide Ba(2)CoGe(2)O(7), we demonstrate the realization of such a directional light-switch function at terahertz frequencies in resonance with the electromagnon absorption. Our results imply that this hidden potential is present in a broad variety of multiferroics.

Dynamics of multiferroic domain wall in spin-cycloidal ferroelectric DyMnO3.

We report the dielectric dispersion of the giant magnetocapacitance (GMC) in multiferroic DyMnO3 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 an extremely high relaxation rate of approximately 10;{7} s;{-1} 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.

Chirality of matter shows up via spin excitations

Chirality is usually manifested by differences in a material’s response to left- and right-circularly polarized light. This difference is the result of the specific distribution of charge within chiral materials. A similar response has now been found to result from the chiral spin structure of an antiferromagnet.

Enhanced infrared magneto-optical response of the nonmagnetic semiconductor BiTeI driven by bulk Rashba splitting.

We study the magneto-optical (MO) response of the polar semiconductor BiTeI with giant bulk Rashba spin splitting at various carrier densities. Despite being nonmagnetic, the material is found to yield a huge MO activity in the infrared region under moderate magnetic fields (up to 3 T). Our first-principles calculations show that the enhanced MO response of BiTeI comes mainly from the intraband transitions between the Rashba-split bulk conduction bands. These transitions connecting electronic states with opposite spin directions become active due to the presence of strong spin-orbit interaction and give rise to distinct features in the MO spectra with a systematic doping dependence. We predict an even more pronounced enhancement in the low-energy MO response and dc Hall effect near the crossing (Dirac) point of the conduction bands.

Generation of Electric Polarization with Rotating Magnetic Field in Helimagnet ZnCr2Se4

Application of magnetic field ( H ) can produce the ferroelectric polarization ( P ) in a proper screw helimagnet, ZnCr 2 Se 4 . While rotating H , we observed the cyclic generation of polarization current arising from the change of P in the conical spin structure. Versatile variations of P in magnitude and sign are observed while changing the direction and magnitude of H . The behaviors are ascribed to the rotation of the spin cones and the conserving or reversing spin-helicity upon the flop of the screw propagation vector, as affected by the competition among the magnetic anisotropy, inclination of the cone axis to H , and the P domain-wall stability.

Cupric chloride CuCl2 as an S=1/2 chain multiferroic

Magnetoelectric properties were investigated for an

101Ru Knight Shift Measurement of Superconducting Sr2RuO4 under Small Magnetic Fields Parallel to the RuO2 Plane

S=1/2

Spin-stretching modes in anisotropic magnets: Spin-wave excitations in the multiferroic ba2coge2o7

chain antiferromagnet