Multi-Triplet Magnons in SrCu2_2(BO3_3)2_2 Studied by Thermal Conductivity Measurements in Magnetic Fields

We have measured the thermal conductivity parallel to the a-axis of the Zn-free and 1% Zn-substituted SrCu$_{2-x}$Zn$_x$(BO$_3$)$_2$ in magnetic fields up to 14 T, in order to examine the thermal conductivity due to the multi-triplet magnons. It has been found that the thermal conductivity peak observed in the spin gap state is suppressed by the substitution of Zn for Cu in high magnetic fields above 6 T, while it is not changed in low magnetic fields below 6 T. The results suggest that the thermal conductivity peak in the spin-gap state of SrCu$_2$(BO$_3$)$_2$ is composed of not only thermal conductivity due to phonons but also that due to the multi-triplet magnons in high fields above 6 T.Comment: 7 pages, 2 figure

Single-crystal growth and dependences on the hole concentration and magnetic field of the magnetic ground state in the edge-sharing CuO2_2 chain system Ca2+x_{2+x}Y2−x_{2-x}Cu5_5O10_{10}

We have succeeded in growing large-size single-crystals of Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$ with $0 \le x \le 1.67$ and measured the magnetic susceptibility, specific heat and magnetization curve, in order to study the magnetic ground state in the edge-sharing CuO$_2$ chain as a function of hole concentration and magnetic field. In $0 \le x \le 1.3$, it has been found that an antiferromagnetically ordered phase with the magnetic easy axis along the b-axis is stabilized and that a spin-flop transition occurs by the application of magnetic fields parallel to the b-axis. The antiferromagnetic transition temperature decreases with increasing $x$ and disappears around $x =$ 1.4. Alternatively, a spin-glass phase appears around $x = 1.5$. At $x = 1.67$ where the hole concentration is $\sim$ 1/3 per Cu, it appears that a spin-gap state is formed owing to the formation of spin-singlet pairs. No sign of the coexistence of an antiferromagnetically ordered state and a spin-gap one suggested in Ca$_{1-x}$CuO$_2$ has been found in Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$.Comment: 13 pages, 12 figures, 1 tabl

Enhanced thermoelectric properties by Ir doping of PtSb2 with pyrite structure

The effects of Ir doping on the thermoelectric properties of Pt1-xIrxSb2 (x = 0, 0.01, 0.03, and 0.1) with pyrite structure were studied. Measurements of electrical resistivity rho, Seebeck coefficient S, and thermal conductivity kappa were conducted. The results showed an abrupt change from semiconducting behavior without Ir (x = 0) to metallic behavior at x = 0.01. The sample with x = 0.01 exhibited large S and low rho, resulting in a maximum power factor (S^2/rho) of 43 muW/cmK^2 at 400 K. The peculiar "pudding mold"-type electronic band dispersion could explain the enhanced thermoelectric properties in the metallic state.Comment: 3 pages, 2 figure

Diurnal variations from muon data at Takeyama underground station

An underground station, Takeyama, is introduced, and some results of the solar diurnal and semi-diurnal variations for the period between 1967 and 1984 are presented. There are clear tendencies of double and single solar cycle variations in the daily variations which are in good accord with those detected by other underground and neutron monitor observations