6 1Ni Mössbauer spectroscopy of magnetic hyperfine interaction in nickel spinels

Abstract

The sign and magnitude of the magnetic hyperfine field in the Ni spinels NiFe2O4, NiCr2O4, NiFe0.3Cr1.7O4, NiRh2O4, and GeNi2O4 were determined by means of 61Ni Mössbauer spectroscopy in external magnetic fields. The hyperfine fields of Ni2+ ions in octahedral lattice sites are negative and of the order of −10 T, and positive for Ni2+ at tetrahedral sites ranging from +2.5 T in NiRh2O4 up to +63 T in NiFe0.3Cr1.7O4. The sign and magnitude of the hyperfine fields are explained in the frame of ligand field theory including the effects of 3d–4p orbital mixing.