Spin glass state and its correlations with the magnetic and electrical properties as well as with the defectiveness in the spinels CuCr 2X 4 (X = S, Se) doped with Sb

Abstract

High degree of defectiveness both in the stoichiometric CuCr 2− x Sb x S 4 ( x = 0.3, 0.4, 0.5) and nonstoichiometric Cu 1 + x Cr 1.5 + y Sb 0.5 + z Se 4 + t (where: −0.02 ≤ x ≤ 0.01, 0.03 ≤ y ≤ 0.35, −0.2 ≤ z ≤ −0.02, 0.01 ≤ t ≤ 0.08) spinels doped with Sb has been determined with the aid of the vacancy model. From the analysis carried out of the effective magnetic moments and the exchange integrals, it follows that in the spinels with sulphur mainly the cation subarrays are defected whereas in the spinels with selenium the defectiveness appears mainly in the anion subarrays. It turned out that in the spinels with sulphur the ferromagnetic cluster spin glass states appear accompanied by the large negative magnetoresistance, whereas in the spinels with selenium the corresponding clusters are antiferromagnetic and the giant magnetoresistance has been observed both positive and negative. A jump-like phase transition was here observed changing both the sign and the measured value of the magnetoresistance from −4433% at 153.2 K up to +980% at 154.24 K. Moreover, in the spinels with selenium both semiconductor–metal and metal–semiconductor phase transitions have been observed from the temperature dependence of the resistance.