Iron chromium antimonates and iron gallium antimonates: preparation, structural and magnetic properties

Abstract

New mixed oxides of composition Fe 1− x Cr x SbO 4 and Fe 1− x Ga x SbO 4 have been prepared. New X-ray powder diffraction data for the compound GaSbO 4 are presented and the decrease in lattice parameters of FeSbO 4 when Fe 3+ is substituted by smaller Cr 3+ or Ga 3+ ions is discussed. The temperature dependence of the inverse magnetic susceptibility of Fe 1− x Cr x SbO 4 at temperatures exceeding ca 200 K follows a Curie-Weiss law. The Curie temperatures and effective magnetic moments decrease with decreasing iron content and are consistent with the substitution of Fe 3+ by Cr 3+ and a reduction in magnetic interaction between cations in the solid. Deviations from the Curie-Weiss law occur at lower temperatures with increasing chromium content and reflect the effect of chromium on the formation of clusters with short-range magnetic order amongst the Fe 3+ species. A second Curie-Weiss law at even lower temperatures and a maximum in the magnetic susceptibility data recorded from Fe 0.85Cr 0.15SbO 4 and Fe 0.63Cr 0.37SbO 4 between 30 and 10 K is indicative of a spin glass-type transition in these materials. The trends in magnetic properties of materials of the type Fe 1− x Ga x SbO 4 are similar, but more marked as a result of the substitution of paramagnetic Fe 3+ by diamagnetic Ga 3+. The 57Fe Mössbauer spectra recorded from Fe 1− x Cr x SbO 4 and Fe 1− x Ga x SbO 4 show an absence of magnetic splitting at 77 K, indicative of faster relaxation times than occur in FeSbO 4. The 121Sb Mössbauer spectra recorded at low temperature show evidence for a super-transferred hyperfine magnetic field on the Sb 5+ ion from iron via oxygen in the iron-rich mixed oxides.