Minoru Soda

Correlation between Spin Helicity and an Electric Polarization Vector in Quantum-Spin Chain Magnet LiCu2O2

Measurements of polarized neutron scattering were performed on a S=1/2 chain multiferroic LiCu2O2. In the ferroelectric ground state with the spontaneous polarization along the c axis, the existence of transverse spiral spin component in the bc plane was confirmed. When the direction of electric polarization is reversed, the vector spin chirality as defined by C_(ij)=S_(i)xS_(j) (i and j being the neighboring spin sites) is observed to be reversed, indicating that the spin-current model or the inverse Dzyaloshinskii-Moriya mechanism is applicable even to this e_(g)-electron quantum-spin system. Differential scattering intensity of polarized neutrons shows a large discrepancy from that expected for the classical-spin bc-cycloidal structure, implying the effect of large quantum fluctuation.

Magnetic Structures of High Temperature Phases of TbBaCo2O5.5

Neutron diffraction studies have been carried out on a single crystal of oxygen-deficient perovskite TbBaCo 2 O 5.5 in the temperature range of 7–370 K. There have been observed several magnetic or...

Electric Control of Spin Helicity in Multiferroic Triangular Lattice Antiferromagnet CuCrO2 with Proper-Screw Order

We have carried out a spin-polarized-neutron study on multiferroic CuCrO 2 to clarify the origin of the ferroelectricity. The neutron results demonstrate that an incommensurate proper-screw magnetic structure of CuCrO 2 induces electric polarization. Not only the magnetic structure but also the oxygen location contributes to the ferroelectricity of CuCrO 2 . The electric polarization of CuCrO 2 can be explained not by a conventional spin-current model but by a theoretical prediction proposed by Arima. The spin helicities of CuCrO 2 can be reversed by the reversal of the electric field E in the multiferroic phase.

Magnetic Correlation of NaxCoO2 and Successive Phase Transitions of Na0:5CoO2 —NMR and Neutron Diffraction Studies—

Data taken by various methods including NMR/NQR and neutron scattering are presented for Na x CoO 2 , particularly Na 0.5 CoO 2 . Attention has also been paid to the x dependence of the electronic nature of this system. The pseudo-gap-like behavior observed in the region of x < x c ∼0.6 is emphasized. For samples with x ≤0.6, signals from two kinds of Co sites with different quadrupole frequencies ν Q of ∼4.1 and ∼2.8 MHz were observed, and the former ν Q , which is nearly equal to that of the superconducting system Na 0.3 CoO 2 · y H 2 O, becomes dominant with decreasing x to 0.3. For Na 0.5 CoO 2 , the Co sites with the larger ν Q have larger magnetic moments. They align antiferromagnetically at T c1 ∼87 K with their direction within the plane, while the Co sites with the smaller ν Q have smaller moments. They align in the direction parallel to the c axis. The ordered moments at the two distinct sites exhibit the same T -dependence, indicating that the existence of these sites is not due to macroscopic ...

Transport and Magnetic Properties of R1-xAxCoO3 (R=La,Pr and Nd; A=Ba,Sr and Ca)

Transport and magnetic measurements have been carried out on perovskite Co-oxides R 1- x A x CoO 3 (R = La, Pr, and Nd; A = Ba, Sr and Ca; 0≤ x ≤0.5: All sets of the R and A species except Nd 1- x Ba x CoO 3 have been studied.). With increasing the Sr- or Ba-concentration x , the system becomes metallic ferromagnet with rather large magnetic moments. For R = Pr and Nd and A = Ca, the system approaches the metal–insulator phase boundary but does not become metallic. The magnetic moments of the Ca-doped systems measured with the magnetic field H =0.1 T are much smaller than those of the Ba- and Sr-doped systems. The thermoelectric powers of the Ba- and Sr-doped systems decrease from large positive values of lightly doped samples to negative ones with increasing doping level, while those of Ca-doped systems remain positive. These results can be understood by considering the relationship between the average ionic radius of R 1- x A x and the energy difference between the low spin and intermediate spin states....

Magnetic Structure of YBaCo4O7 with Kagome and Triangular Lattices

Neutron diffraction studies have been carried out in the temperature(T) range between 10 K and 130 K on a single crystal of YBaCo4O7, which has the stacking of kagome and triangular lattices of CoO4 tetrahedra along the c-axis. Structural transitions have been found at two temperatures Tc1~70 K and Tc2~105 K. With decreasing T, magnetic order appears along with the transition at Tc2, but it does not grow to an ideal long-range order even at the lowest T studied (~10 K). Two groups of magnetic diffuse reflections, which originate from the Co-moments of the kagome and triangular lattices, are observed separately in the reciprocal space. With further decreasing T, the growth rates of the intensities of these two are enhanced by another transition at Tc1. These magnetic behaviors seem to be related to the release of the geometrical frustration. At 10 K, the patterns of the magnetic short-range order have been determined for both sites of the kagome and triangular lattices.

Electric polarization induced by a proper helical magnetic ordering in a delafossite multiferroic Cu Fe 1 − x Al x O 2

We have established the relationship between the electric polarization vector and the local spin arrangement including vector spin chirality in delafossite multiferroic

Ferromagnetic Transition of Pyrochlore Compound Yb2Ti2O7

\mathrm{Cu}{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}{\mathrm{O}}_{2}

Spin–Glass-like Transition and Hall Resistivity of Y2-xBixIr2O7

. The results of polarized neutron diffraction and pyroelectric measurements demonstrate that proper helical magnetic ordering in

Spin-nematic interaction in the multiferroic compound Ba2CoGe2O7.

\mathrm{Cu}{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}{\mathrm{O}}_{2}