I.V. Medvedeva

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.

Hydrostatic pressure effect on the metal-insulator transition in sulfur deficient BaCo0.9Ni0.1S2−y

The resistivity versus temperature curves of three BaCo0.9Ni0.1S2−y samples with different sulfur content have been measured for 77 K < T < 300 K and under pressures up to 5 kbar. The study shows that the action of hydrostatic pressure on the metal-insulator transition is qualitatively similar to a decrease of y, which can be represented as crystal pressure. An estimate of the volume lattice contraction both under pressure and with y-decrease shows that an important feature of this M-I transition might be the existence of a critical unit cell volume.