A thiospinel CuIr 2 S 4 exhibits a temperature-induced metal-insulator (M -I) transition at 230 K with a simultaneous spin-dimerization and charge-ordering transition although a three-dimensional system. On the other hand, CuCr 2 S 4 has the same spinel structure without any structural transformations. CuCr 2 S 4 remains metallic and is ferromagnetic with the Curie temperature T C Ӎ377 K. In order to see the effect of substituting Cr for Ir on the M -I transition, we have carried out a systematic experimental study of electrical and magnetic properties of Cu(Ir 1Ϫx Cr x ) 2 S 4 system. The M -I transition temperature decreases steeply with increasing Crcomposition x and this transition is not detected above xӍ0.05. The value of T C decreases with decreasing x from 1.0, then T C disappears below xӍ0.20. The ferromagnetic state suggests the non-collinear spin alignment. In the intermediate composition range over xϭ0.08 to 0.20, the B-site undergoes a local crystal distortion around 180 K, where the energy level t 2g splits into lower symmetry. Then the low-spin state within the t 2g subspace is realized for Cr 3ϩ ion with sϭ1/2. The magnetic state of Cr 3ϩ ion indicates a crossover from high temperature sϭ3/2 to low temperature sϭ1/2 state around 180 K.
The study goal was to establish a standard industrial procedure for the measurement of thermal effusivity by a thermal microscope (TM), using a periodic heating method with a thermoreflectance (TR) technique. To accomplish this goal, a working group was organized that included four research institutes. Each institute followed the same procedure: a molybdenum (Mo) film was sputtered on the surface of Pyrex, yttria-stabilized zirconia (YSZ), alumina (Al 2 O 3 ), Germanium (Ge), and silicon (Si) samples, and then the phase lag of the laser intensity modulation was measured by the resultant surface temperature. A procedure was proposed to calibrate the effect of 3D heat flow, based on the analytical solution of the heat conduction equation, and thermal effusivity was measured. The derived values show good agreement with literature values. As a result, the TM calibration procedure can be recommended for practical use in measuring the thermal effusivity in a small region of the materials.
We have studied the electronic structure and its changes across the charge-density-wave ͑CDW͒ transition in spinel-type CuV 2 S 4 by photoemission spectroscopy and first-principles band-structure calculations. The photoemission spectra show pseudogap-like behavior and the gap size is estimated to be ϳ90 meV. The large energy scale of the pseudogap compared to the transition temperature and its anomalous temperature dependence implies that the involved interaction is in the strong-coupling regime. The calculated electronic susceptibility (q) shows a small peak at qӍ 11 40 ͓110͔, which is consistent with the observed wave vector q Ӎ 1 4 ͓110͔ characterizing the CDW. This result suggests that Fermi surface nesting is at least partly responsible for the CDW formation.
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