Structural, magnetic and electronic properties of Fe0.5Cu0.5Cr2S4

Abstract

The crystallographic and magnetic structures of Fe _0.5 Cu _0.5 Cr ₂ S ₄ have been examined in order to generate a possible mechanism to explain the CMR behaviour of such spinels. Neutron powder diffraction has revealed that the tetrahedrally coordinated Fe ³⁺ and Cu ⁺ ions are fully ordered, with the magnetic moments of Fe ³⁺ (µ ₃₀₀ =–1.97(5) µ _B ) aligned antiparallel to those of the octahedrally coordinated Cr ³⁺ (µ ₃₀₀ =1.49(3) µ _B ). The results suggest a new CMR mechanism, which involves exchange on three cation centres (‘triple exchange’) and requires antiferromagnetic coupling of magnetic spins, in contrast to the manganite perovskites for which double-exchange provides a ferromagnetic state.