Magnetic properties of the spinel-type Cu(Cr1-xHfx)2S4

The spinel sulphide CuCr2S4 is a metallic ferromagnet with a Curie temperature Tc similar or equal to 380 K, while CuHf2S4 has no magnetic anomaly. Magnetic properties of the quaternary spinel-type Cu(Cr1-xHfx)(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 similar or equal to 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 Cr3+ ions. (C) 2009 Elsevier Inc. All rights reserved.