209 research outputs found

    The Lorenz number in CeCoIn5_5 inferred from the thermal and charge Hall currents

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    The thermal Hall conductivity κxy\kappa_{xy} and Hall conductivity σxy\sigma_{xy} in CeCoIn5_5 are used to determine the Lorenz number LH{\cal L}_H at low temperature TT. 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 TT, 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 σxy\sigma_{xy}.Comment: 6 pages, 7 figures Intro para slightly lengthened. Added 2 new re

    Specific heat study of spin-structural change in pyrochlore Nd2_2Mo2_2O7_7

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    By measurements of specific heat, we have investigated the magnetic field (HH) induced spin-structural change in Nd2_2Mo2_2O7_7 that shows spin-chirality-related magneto-transport phenomena. A broad peak around 2 K caused by the ordering of 2-in 2-out structure of the Nd moments at zero HH shifts to the lower temperature (TT) up to around 3 T and then to the higher TT above around 3 T with increasing HH for all the direction of HH. This is due to the crossover from antiferromagnetic to ferromagnetic arrangement between the Nd and Mo moments. While the peak TT increases monotonically above 3 T for HH//[100], another peak emerges around 0.9 K at 12 T for HH//[111], which is ascribed to the ordering of 3-in 1-out structure. For HH//[110], a spike like peak is observed at around 3 T, which is caused perhaps by some spin flip transition.Comment: 5 pages, 4 figure

    Impurity-doping induced ferroelectricity in frustrated antiferromagnet CuFeO2

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    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.Comment: 4 pages, 4 figure

    Ferroelectricity induced by spin-dependent metal-ligand hybridization in Ba2_2CoGe2_2O7_7

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    We have investigated the variation of induced ferroelectric polarization under magnetic field with various directions and magnitudes in a staggered antiferromagnet Ba2_2CoGe2_2O7_7. 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 pp-dd 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