ternary sulfides. Neutron diffraction data from powders was collected on the 3T2 diffractometer at the Laboratoire LØon Brillouin, Saclay, France, to follow the crystal and magnetic structures of the title compound as a function of temperature. Rietveld refinements made use of the FullProf Rietveld program [18].
Variable-temperature Mössbauer spectra with good statistics were measured from 300 K down to 4.2 K using a source of 57 Co in rhodium. The data were collected with the sample in a helium cryostat. The program MOSFUN [19] was used to analyze the data.
First principles calculations of the electronic structures were performed using the LMTO-ASA method. A detailed description of the LMTO-ASA method, including its applications, can be found elsewhere [20]. The scalar± relativistic Kohn Sham equations were solved, taking all relativistic effects into account except for spin±orbit coupling. The basis set included the s, p, and d wavefunctions for Fe, Cu, Cr, and S. The S d wavefunctions were treated using the down-folding procedure. The k integrated functions were evaluated by the tetrahedron method on a grid of 735 k points in the irreducible part of the Brillouin zone (1/48 of the BZ). We used lattice constants from the neutron diffraction refinement and constructed a supercell with an ordered arrangement of Fe and Cu on the tetrahedral sites in the space group F43m. For comparison, we have also performed calculations on the end members in the series, that is FeCr 2 S 4 and CuCr 2 S 4 .
Because of magnetic ordering, the calculations were performed (using the von Barth±Hedin [21] form of the exchange correlation within the local spin density approximation) with the assumption of a magnetic ground state (spin-polarized calculation) as these, in agreement with experiment, yielded more stable total energies.