CRYSTALLOGRAPHIC AND MAGNETIC-PROPERTIES OF ANTIFERROMAGNETIC CU0.5FE0.5RH2S3.4SE0.6

The effects of selenium impurities on the crystallographic and magneti c properties of Cu0.5Fe0.5Rh2S4 have been studied by Mossbauer spectro scopy, X-ray diffraction, and magnetic-susceptibility measurement. A 1 5% replacement of sulphur ions by selenium ions increases the lattice constant ao of the cubic spinel structure by 0.45%. The iron ions are in ferric states and occupy the tetrahedral sites. The temperature dep endence of the magnetic hyperfine fields at the three different sites follows the Brillouin function for S = 5/2. The 0.45% increase of inte ratomic separation results in a decrease of the Neel temperature, the paramagnetic Neel temperature, and the Debye temperature by 37, 9, and 31%, respectively. The longer-range superexchange interaction between second-nearest Fe neighbors is weakened much more by the increase of the interatomic separation than that between first-nearest Fe neighbor s.