Versatile and gigantic magnetoelectric (ME) phenomena have been found for a single crystal of DyFeO3. Below the antiferromagnetic ordering temperature of Dy moments, a linear-ME tensor component as large as alphazz approximately 2.4 x 10(-2) esu is observed. It is also revealed that application of magnetic field along the c axis induces a multiferroic (weakly ferromagnetic and ferroelectric) phase with magnetization [> or =0.5 microB/formula unit (f.u.)] and electric polarization (> or =0.2 microC/cm2) both along the c axis. Exchange striction working between adjacent Fe3+ and Dy3+ layers with the respective layered antiferromagnetic components is proposed as the origin of the ferroelectric polarization in the multiferroic phase.

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Subcortical white matter (WM) is a frequent target of ischemic injury and extensive WM lesions are important substrates of vascular cognitive impairment (VCI) in humans. However, ischemic stroke rodent models have been shown to mainly induce cerebral infarcts in the gray matter, while cerebral hypoperfusion models show only WM rarefaction without infarcts. The lack of animal models consistently replicating WM infarct damage may partially explain why many neuroprotective drugs for ischemic stroke or VCI have failed clinically, despite earlier success in preclinical experiments. Here, we report a novel animal model of WM infarct damage with cognitive impairment can be generated by surgical implantation of different devices to the right and left common carotid artery (CCA) in C57BL/6J mice. Implantation of an ameroid constrictor to the right CCA resulted in gradual occlusion of the vessel over 28 d, whereas placement of a microcoil to the left CCA induced ϳ50% arterial stenosis. Arterial spin labeling showed a gradual reduction of cerebral blood flow over 28 d post operation. Such reductions were more marked in the right, compared with the left, hemisphere and in subcortical, rather than the cortical, areas. Histopathological analysis showed multiple infarct damage in right subcortical regions, including the corpus callosum, internal capsule, hippocampal fimbria, and caudoputamen, in 81% of mice. Mice displaying such damage performed significantly poorer in locomotor and cognitive tests. The current mouse model replicates the phenotypes of human subcortical VCI, including multiple WM infarcts with motor and cognitive impairment.

Dielectric responses have been investigated on the triangular-lattice antiferromagnet CuFeO2 and its site-diluted analogs CuFe1−xAlxO2 (x=0.01 and 0.02) with and without application of magnetic field. We have found a ferroelectric behavior at zero magnetic field for x=0.02. At any doping level, the onset field of the ferroelectricity always coincides with that of the noncollinear magnetic structure while the transition field dramatically decreases to zero field with Al doping. The results imply the further possibility of producing the ferroelectricity by modifying the frustrated spin structure in terms of site-doping and external magnetic field. In all these materials, the ferroelectric behavior is observed in the noncollinear magnetic phase. Katsura et al. proposed the spin current theory for the origin of ferroelectricity in the noncollinear magnetic phase [9]. In the theory, the electric dipole is induced by the spin current, which is expected to flow between noncollinear magnetic moments in analogy to the magnetic dipole induced by electric current. To produce such a ferroelectricity of magnetic origin, modification or partial lifting of spin state degeneracy may be prerequisite with use of the frustrated spin systems.Delafossite CuFeO 2 (See Fig. 1(d) for the structure) is one of candidates for such magnetic ferroelectrics. The crystal structure is characterized by the space group R3m, with two-dimensional triangular lattice layers stacked rhombohedrally along the caxis ( Fig. 1(d)). The magnetic structure of this material has been studied extensively by neutron diffraction measurements [10,11,12,13,14,15]. At zero field, a 4-sublattice collinear structure (CM-4) is observed at the lowest temperature. When the field is increased up to 7 T, a noncollinear spin structure (NC) emerges [16]. Above 12 T, a 5-sublattice collinear structure (CM-5) is realized [11]. Recently, Kimura et al. reported that the spontaneous polarization is observed in the noncollinear magnetic phase in between the 4-sublattice and 5-sublattice phases [18]. Similarly to the magnetic field, Al doping is known to easily modify the magnetic structure [13]. The 2 % substitution of Fe with Al induces the transition from CM-4 to NC at zero field and low temperature [12]. To clarify the relation between the magnetic structure and dielectric properties, the search for electric polarization is desirable also for the Al-doped crystals. In this work, we report the finding of ferroelectricity in the noncollinear magnetic phase of the Al doped crystal even in the absence of external magnetic field as well as the systematic evolution of the magneto-electric phase with Al-doping. This ensures the close relation between the noncollinear magnetic structure and ferroelectricity.Single crystals of CuFe 1−x Al x O 2 (x=0.00, 0.01, 0.02) were prepared by a floating zone method [19]. For the measurements of pyroelectric current and dielectric constant, the crystals were cut into thin planes with the widest faces parallel to (110) plane. As the electrodes, we ...

We have investigated the dielectric response in an antiferromagnetic dimer-Mott insulator β'-(BEDT-TTF)2ICl2 with square dimer lattice, compared to a spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3. Temperature dependence of the dielectric constant shows a peak structure obeying Curie-Weiss law with a strong frequency dependence. We found an anisotropic glassy ferroelectricity by pyrocurrent measurements, which suggests the charge disproportionation resulting in an electric dipole in a dimer. Each ferroelectric and antiferromagnetic transition temperatures is closely related to the antiferromagnetic interaction energy and a freezing temperature of dipole dynamics in a dimer, respectively. These correspondences suggest the possible charge-spin coupled degrees of freedom in the system.