S. Iguchi

Impurity-doping-induced ferroelectricity in the frustrated antiferromagnet CuFe O2

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. PACS numbers: 75.80.+q, 77.80.-e, 75.30.Kz, 75.50.Lk The ferroelectricity in magnetic materials has been attracting much attention because of possibility of showing gigantic magneto-electric effects[1, 2, 3], as stimulated by the discovery of the electric polarization flop induced by a magnetic field in TbMnO3[4]. Similar ferroelectric behaviors have recently been discovered in several spin-frustrated systems; Ni3V2O8[5], Ba0.5Sr1.5Zn2Fe12O22[6], CoCr2O4[7], and MnWO4[8]. 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.

Spin-lattice coupling in ferroelectric spiral magnets : Comparison between the cases of (Tb,Dy)MnO3 and CoCr2O4

Lattice modulation expected for various types of spiral magnetic ordering with a propagation vector Q m is discussed in terms of the symmetric ( S i · S j type) and antisymmetric ( S i × S j type) ...

Emergence of charge degrees of freedom under high pressure in the organic dimer-Mott insulator β′-(BEDT - TTF) 2 ICl 2

To elucidate the pressure evolution of the electronic structure in an antiferromagnetic dimer-Mott (DM) insulator

Interface-dependent magnetotransport properties for thin Pt films on ferrimagnetic Y3Fe5O12

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Crystallization and vitrification of electrons in a glass-forming charge liquid

-(BEDT-TTF)

Quantum-disordered state of magnetic and electric dipoles in an organic Mott system

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Polaronic Behavior of Photoelectron Spectra of Fe3O4 Revealed by Both Hard X-ray and Extremely Low Energy Photons

ICl

Collective excitation of a short-range charge ordering inθ-(BEDT-TTF)2CsZn(SCN)4

_2

Magneto-optical effect induced by spin chirality of the itinerant ferromagnet Nd2Mo2O7

, which exhibits superconductivity at 14.2 K under 8 GPa, we measured the polarized infrared (IR) optical spectra under high pressure. At ambient pressure, two characteristic bands due to intra- and interdimer charge transfers have been observed in the IR spectra, supporting that this salt is a typical half-filled DM insulator at ambient pressure. With increasing pressure, however, the intradimer charge transfer excitation shifts to much lower energies, indicating that the effective electronic state changes from half-filled to 3/4-filled as a result of weakening of dimerization. This implies that the system approaches a charge-ordered state under high pressure, in which charge degrees of freedom emerge as an important factor. The present results suggest that charge fluctuation inside of dimers plays an important role in the high-temperature superconductivity.

Mesoscopic 2D Charge Transport in Commonplace PEDOT:PSS Films

We have studied magnetoresistance and Hall effects for 1.8-nm-thick Pt films grown on a ferrimagnetic insulator Y3Fe5O12 in a wide temperature (0.46-300 K) and magnetic-field (-15-15 T) region. In the low-temperature regime where quantum corrections to conductivity are observed, weak antilocalization behavior observed in Pt films is critically suppressed when the film is attached to Y3Fe5O12. Hall resistance in the Pt film is also affected by Y3Fe5O12, and it exhibits logarithmic temperature dependence in a broad temperature range. The magnetotransport properties in the high-field range are significantly influenced by the interface between Pt and Y3Fe5O12.