Data taken by various kinds of methods including NMR/NQR and neutron scattering are presented for Na x CoO 2 , in particular, for Na 0.5 CoO 2 . Attentions have also been paid to the x dependence of the electronic nature. The pseudo-gap-like behavior observed in the region of x

We have prepared the superconducting system LaFe 1-y Co y AsO 1-x F x (x=0.11) and carried out measurements of their electrical resistivities ρ and superconducting diamagnetisms.75 La-NMR studies have also been carried out. The Knight shift observed for 75 As has been found to be suppressed by the superconductivity, while for 135 La, the shift is almost insensitive to the superconductivity. This result presents rather strong experimental evidence for the singlet pairing. The Co-doping effect on the superconducting transition temperature T c is not so significant as expected for superconductors with nodes, suggesting that the potential scattering does not seem to primarily suppress the superconductivity. Even for superconductors without nodes, it may not be so trivial to expect this small effect, if there are two different (disconnected) Fermi surfaces whose order parameters have opposite signs. As a possible explanation of the observed T c suppression, which is found to be small, seems to be related with the loss of the itinerant nature of the electrons..

Neutron scattering studies and measurements of the dielectric susceptibility ε and ferroelectric polarization P have been carried out in various magnetic fields H for single-crystal samples of the multiferroic system LiVCuO 4 with quasi one-dimensional spin 1/2 Cu 2+ chains formed of edge-sharing CuO 4 square planes, and the relationship between the magnetic structure and ferroelectricity has been studied. The ferroelectric polarization is significantly suppressed by the magnetic field H above 2 T applied along a and b axes. The helical magnetic structure with the helical axis parallel to c has been confirmed in H=0, and for H//a, the spin flop transition takes place at H=2 T with increasing H, where the helical axis changes to the direction parallel to H. The ferroelectric polarization along a at H=0 is found to be proportional to the neutron magnetic scattering intensity, indicating that the magnetic order is closely related to the appearance of the ferroelectricity. The relationship between the magnetic structure and ferroelectricity of LiVCuO 4 is discussed by considering the existing theories. dependence of the magnetic susceptibility, the broad peak attributed to the growth of the short-range spin correlation, typical for low-dimensional antiferromagnets, is observed at ~26 K and the sharp anomaly is observed at the transition temperature T N =2.4 K, which corresponds to the 3D long-range magnetic order. For this system, the exchange interaction between the nearest-neighbor Cu 2+ ions, J 1 is rather weak (Cu-O-Cu angle is ~95°), or even weaker than the next-nearest-neighbor interaction J 2 , suggesting that effects of the magnetic frustration are significant in its magnetic properties. Enderle et al. reported that J 1~-12 K (ferromagnetic) and J 2~4 1 K (antiferromagnetic) by the studies of magnetic excitation using inelastic neutron scattering. 8) Due to the magnetic frustration, the magnetic structure below T N is expected not to be trivial. Actually, the magnetic structure of LiVCuO 4 reported by Gibson et al. 9) is helical with the moments in the ab-plane (in the CuO 4 square planes) and with the incommensurate modulation vector along b. Based on the 7Li-NMR spectra, the magnetic structure in the applied magnetic field was also discussed.10) The authors' group reported a clear anomaly at T N in the T-dependence of the dielectric susceptibility ε for the electric field E//a, indicating that the ferroelectric transition takes place simultaneously with the magnetic transition. 6)In the present work, neutron scattering and measurements of dielectric susceptibility ε and ferroelectric polarization P have been carried out on single-crystal samples of LiVCuO 4 in the various magnetic fields. Based on results of these studies, the relationship between magnetic structure and ferroelectricity for LiVCuO 4 is discussed, in relation to the theoretical models on the occurrence of the multiferroic state. 11-16)Single-crystal samples of LiVCuO 4 used in the measurements of ε and P were grown by a flux method, as re...

Neutron diffraction studies have been carried out in the temperature(T) range between 10 K and 130 K on a single crystal of YBaCo 4 O 7 , which has the stacking of kagome and triangular lattices of CoO 4 tetrahedra along the c-axis. Structural transitions have been found at two temperatures T c1 ∼70 K and T c2 ∼105 K. With decreasing T, magnetic order appears along with the transition at T c2 , 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 T c1 . 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.

Received)Neutron diffraction and 7 Li-NMR have been applied to determine the multiferroic system LiCu 2 O 2 , which has four chains (ribbon chains) of edge-sharing CuO 4 square planes in a unit cell. We have confirmed that there are successive magnetic transitions at T N1 =24.5 K and T N2 =22.8 K. In the T region between T N1 and T N2 , the quasi one-dimensional spins (S=1/2) of Cu 2+ ions within a chain have a collinear and sinusoidally modulated structure with Cu-moments parallel to the c-axis and with the modulation vector along the b-axis. At T < T N2 , an ellipsoidal helical spin structure with the incommensurate modulation has been found. Here, we present detailed parameters, describing the modulation amplitudes, helical axis vectors as well as the relative phases of the modulations of four ribbon chains, which can well reproduce both the NMR and neutron results in the two magnetically ordered phases. This finding of the rather precise magnetic structures enables us to discuss the relationship between the magnetic structure and the multiferroic nature of the present system in zero magnetic field, as presented in our companion paper (paper I), and open a way how to understand the reported electric polarization under the finite magnetic field.