Ryo Endoh

Resistance and susceptibility anomalies in IrTe{sub 2} and CuIr{sub 2}Te{sub 4}

AbstractIrTe2has the CdI2structure and CuIr2Te4has a defect-NiAs structure at room temperature. Both compounds show basically metallic behavior. Magnetic and resistance anomalies, showing a hysteresis in temperature, have been found in IrTe2and CuIr2Te4. On heating, the resistivity ρ exhibits a hump-shaped maximum around 270 and 250 K for IrTe2and CuIr2Te4, respectively. The magnetic susceptibility χ reveals a step-like anomaly which gives evidence of a difference in the value of the Pauli paramagnetism between the high- and low temperature sides, corresponding to the anomalous behavior in ρ. These anomalies of ρ and χ in IrTe2originate from a gradual structure deformation with temperature, where the crystal symmetry changes from high temperature trigonal

Electronic heat capacity of CuIr2Se4 at low temperature

P\overline 3 m1

Metal-insulator transition and superconductivity in the spinel-type Cu(Ir1-xRhx)2S4 system

to low temperature monoclinic C2/m.

Ferromagnetism and the metal-insulator transition in the thiospinel Cu(Ir1-xCrx)2S4

Abstract The magnetic susceptibility of the garnet-type single crystal Tm3Al5O12 exhibits the typical Van Vleck temperature independent paramagnetism below ≈8 K. The temperature dependence of the susceptibility over the range 2.0–300 K has been analyzed on the assumption that the cubic crystal-electric-field dominates the energy level on 3H6 (J=6) ground multiplet for Tm3+ ion having 12-electrons in 4f shell. The ground state of the 3H6 is nonmagnetic with Γ2 singlet, avoiding the Kramers doublet. The energy separation between Γ2 and the first excited state Γ(2)5 triplet is evaluated to be 68.0 K. The whole energy interval Δ between Γ2 and the highest state Γ1 in 3H6 is estimated to be 339.5 K.

Metal-insulator transition in the spinel-type Cu(Ir1−xCrx)2S4 system

Abstract The normal thiospinel CuIr2S4 exhibits a temperature-induced metal–insulator (M–I) transition around 230 K with structural transformation. A charge-ordering and spin-dimerization transition in CuIr2S4 has been found recently. In contrast to CuIr2S4, CuIr2Se4 remains metallic down to 0.4 K without the M–I transition. The instability of the metallic state in CuIr2Se4 at high pressure has been previously reported. Heat capacity of CuIr2Se4 has been now measured over the temperature range of 0.5– 11 K . The fit of the heat capacity data to C=γT+βT3 is very good with γ=6.68 mJ mol f.u. −1 K −2 and β=4.09 mJ mol f.u. −1 K −4 , where γT is the electronic heat capacity.

Electronic structure of Cu1-xNixRh2S4 and CuRh2Se4: Band-structure calculations, x-ray photoemission, and fluorescence measurements

Abstract The normal sulphospinel CuIr2S4 exhibits a temperature-induced metalinsulator (M-I) transition around T M-1 = 230 K with a structural transformation. This T M-1 increases markedly with increasing pressure. It has been verified that the 5d electrons of Ir ions at the B sites located at the Fermi surface play a significant role for the strong correlated electron system. Conversely, CuTi2S4 remains metallic down to 4.2 K without any structural transformations. These two compounds have the same normal spinel structure, whereas the number of d electrons at the B sites are quite different. High-purity spinel-type Cu(Iri1−xTix)2S4 specimens have been successfully synthesized. The value of the lattice constant a indicates a broad minimum around x = 0.12, not obeying Vegards law. We have systematically studied the structural transformation and electrical and magnetic properties of Cu(Ir1−xTix)2S4. A phase diagram between T M-1 and x will be provided for the Cu(Ir1−xTix)2S4 system. T M-1 varies drastically with x and disappears at around x = 0.06. A novel relationship, namely a ‘mirror image effect’, between the value of residual resistivity and the magnitude of the electronic density of states, D(εF), at the Fermi level, has been observed accurately.