On the cation distribution in Ni1−xCuxFe2−yAlyO4 spinels

Abstract

Two spinel solid solution series, Ni1−xCuxFe2−yAlyO4 with y=0.6 and 1.0, where 0.0⩽x⩽1.0 have been investigated by x-ray diffractometry and Mössbauer spectroscopy. Lattice, hyperfine parameters, and cation distribution among the two distinct crystallographic sites as a function of Cu2+ and Al3+ substitution are determined. Mössbauer 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.