Magnetic properties of the spinel-type [formula omitted

Abstract

The spinel sulphide CuCr 2 S 4 is a metallic ferromagnet with a Curie temperature T c ≃ 380 K , while CuHf 2 S 4 has no magnetic anomaly. Magnetic properties of the quaternary spinel-type Cu ( Cr 1 - x Hf x ) 2 S 4 system have been studied. With increasing x the ferromagnetic properties are weakened gradually from a predominant ferromagnetic, a spin-glass, finally to a simple paramagnetic behavior. For the composition of x ≃ 0.50 , a re-entrant spin-glass phase could emerge, even though the Curie temperature is ill-defined as a ferromagnetic phase boundary. Specimens with x ≥ 0.90 remain paramagnetic down to 4.2 K. A spin crossover phenomenon is found around 160 K in the specimens of x = 0.50 – 0.70 . A step-like anomaly is manifestly detected in the magnetization, which corresponds with the change of the spin state. This crossover indicates that the spin state converts from high temperature S = 2 into low temperature S = 3 2 states. In the ordered states in T < 160 K , the magnetic moment originates from only Cr 3 + ions.