Electronic and magnetic structure of Fe ions in NiCr2S4

The magnetic semiconductor NixFe1−xCr2S4 (x=0.985, 0.97, 0.96) has been investigated over the temperature range from 12 to 600 K using a Mossbauer technique. The electronic structure of Fe ions in NiCr2S4 was calculated with the Hamiltonian incorporating free‐ion term, axial and rhombic crystal field, spin‐orbital couplings, and exchange interactions. The ground orbital state is separated by 9.64 ‖λ‖ from the first excited state, thereby making the quadrupole splitting somewhat insensitive to temperature. Using x‐ray crystallographic data, the contribution of direct lattice sum to the electric‐field gradient has been considered. In calculating the temperature dependence of quadrupole splitting, the axial field parameter Δ1=−3.0‖λ‖, the rhombic field parameter Δ2=−2.8‖λ‖, and the covalency factor α2=0.73 in Ni0.985Fe0.015Cr2S4 were determined. Magnetic hyperfine and quadrupole interactions in the antiferromagnetic state of Ni0.96Fe0.04Cr2S4 at 12 K have been studied, yielding the following results: H=147.8...