Diamagnetic nuclear Sn-119 probes in the copper chromites CuCr2X4 (X = O, S, Se) with a spinel structure

The CuCr2X4 (X = O, S, Se) spinel system has been studied by the Mossbauer spectroscopy of the nuclear diamagnetic Sn-119 probe at low temperatures in an external magnetic field. The hyperfine magnetic fields H-Sn induced by paramagnetic ions at tin nuclei in the CuCr2S4 and CuCr2Se4 chalcogenides have giant values and are somewhat higher than those detected in the CuCr2O4 oxide. This behavior is caused by the strong covalence of the chalcogenides, which is supported by the experimentally found isomer shifts. The H-Sn field is found to be mainly contributed by superexchange 90 degrees interactions in the B-sublattice along the Cr[B]-X-Sn[B] bond chain, whose role increases in the series O-S-Se. In the oxygen CuCr2O4 spinel, the partial contributions to the H-Sn field induced by the Cu2+ and Cr3+ ions are estimated. The local magnetic structure of the CuCr2O4 spinel is refined, and its total magnetization is shown to be directed along the magnetic moment of copper in the A sublattice