Temperature dependence of the hyperfine fields in NiFe2O4 and CuFe2O4 oxides

摘要

We report the temperature dependence of the magnetic properties of (Ni, Cu)Fe2O4 spinel oxides. Mossbauer spectra for NiFe2O4 at various temperatures (79 <= T <= 900 K) are well fitted by two sextets associated with Fe-57 nuclei at tetrahedral (A) and octahedral (B) sites. The Curie point T-C was deduced by zero velocity Mossbauer technique to be 873 +/- 3 K. The hyperfine fields are observed to vary with temperature according to the equation B-hf(T) = B-hf(0)[1 - (T/T-C)(n)](beta n) where n=1 (based on the Landau-Ginzburg theory) and n=2 (based on the Stoner theory). A systematic decrease of the Mossbauer spectrum shift with increasing temperature is observed.