On the cation distribution in Ni1-xCuxFe2-yAlyO4 spinels

Two spinel solid solution series, Ni1-xCuxFe2-yAlyO4 with y = 0.6 and 1.0, where 0.0 less than or equal to x less than or equal to 1.0 have been investigated by x-ray diffractometry and Mossbauer spectroscopy. Lattice, hyperfine parameters, and cation distribution among the two distinct crystallographic sites as a function of Cu2+ and Al3+ substitution are determined. Mossbauer effect (ME) spectra at 293 K for compositions with y = 0.6 consist of one sextet for A sites, and three sextets for B sites due to different fields at Fe nuclei. On the other hand, the ME spectra for the compounds with y = 1.0 in the ferrimagnetic state at (293 and 77 K) show only one sextet for Fe3+ at A site giving clear evidence for a completely inverse spinel with Ni, Cu, and Al ions occupying B sites. ME parameters are deduced and analyzed for all studied compounds, where the observed hyperfine fields are explained on the basis of the superexchange and supertransferred hyperfine interactions. (C) 1999 American Institute of Physics. [S0021-8979(99)06701-8].