Correlation between structural and magnetic properties of half‐metallic spinel CuV 2 S 4 due to the order–disorder transition of 3d 2 (t 2g ) orbitals of V 3+ ions

Structural and magnetic properties of the spinel CuV 2 S 4 have been studied by means of X‐ray diffraction using synchrotron radiation and measurements of magnetic susceptibility. The structural phase transitions occur at about 55 K and 90 K, and the superlattice reflections ( h ± q o , k ± q o , l ) having an orthorhombic reduced wavevector q o = (1/4, 1/4, 0) are observed at 10 K. This suggests that the structure below 55 K is a commensurate unit cell of 4 a p × 4 b p × c p , where the subscript ‘p’ means a pseudo‐spinel structure, and that the structural phase transitions are induced by the cooperative displacement of S ions in one‐dimensional VS 6 octahedral chains, which are aligned along an orthorhombic [110] direction. The susceptibility also shows that the weak ferromagnetic transition occurs at about 90 K, and the spike‐like susceptibility is observed in the region of about 40 K and 55 K. The unusual electronic and magnetic properties of CuV 2 S 4 in the low‐temperature phases below about 90 K are interpreted by order and disorder states of (3d xy , 3d yz , 3d zx ) for the V 3+ 3d 2 (t 2g ) orbitals in the VS 6 octahedral chains. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)