P. Mandal

Order parameter of the metal to insulator phase transition in the thio spinel CuIr2S4

The temperature dependences of the resistivity, the magnetoresistance and the Hall effect of the Mott compound CuIr2S4−y have been measured through the metal insulator transition temperature Tmi, in the temperature range 4.2 K<T<300 K and in magnetic fields up to 5 Tesla. We observed carrier concentrations of 1020cm−3 in the insulating and of 1022 cm−3 in the metallic state. Anomalies in the resistivity curve ρ(T), an anomalous shift of Tmi in magnetic fields, dTmi/dH=+0.3 K/T, and a structure of the magnetoresistance close to Tmi were observed and interpreted in terms of quasi-particle formation.

EPR spectra of CuIr2S4

Abstract The hole-like character of the EPR-signals at g eff =2.25 and 2.06 which are observed in all CuIr 2 S 4 samples suggests structural defects which are related to the breaking of covalent bonds. The broad EPR signal around g eff =2.00 is related very likely to sulfur–sulfur bonds or sulfur chain endstates, which vary from sample to sample in a distinct manner.

Heat Diffusivity of the Mott Systems BaCo0.9Ni0.1S2—y and CuIr2S4

The thermal diffusivity D(T), the Seebeck-coefficient S(T) and specific heat capacity c p (T) of BaCo 0.9 Ni 0.1 S 2-y and of CuIr 2 S 4 were investigated in the temperature range 100 K < T < 350 K and in particular through their metal-insulator transition at T MI . We find steps in S(T); D( T) and in the heat conductivity K( T) at T MO = 230 and 228 K, respectively. In particular, for BaCo 0.9 Ni 0.1 S 1.95 , we find a step in K of almost one order of magnitude. Since a large pressure shift had been discovered earlier for BaCo 0.9 Ni 0.1 S 1.9 , these crystals are potential pressure activated heat switches.

Anomalous Metal–Insulator Transition in BaCo1—xNixS2—y as a Triggered Phase Transition

The anomalous metal-insulator transition in BaCo 1-x Ni x S 2-y is identified as a triggered phase transition based on strong coupling between a magnetic and a structural order parameter. In particular, we observe a second-order paramagnetic-antiferromagnetic transition at T N followed by a first-order metal-insulator transition at T MI . The field-induced shifts of the sequential transition temperatures are determined for y = 0.05: dT N /dB = (-0.8 ± 0.2) K/T, and (-0.1 ± 0.1) K/T ≤ dT MI /dB ≤ (-0.5 ± 0.1) K/T.