ELECTRONIC AND MAGNETIC-STRUCTURE OF FE IONS IN NICR2S4

The magnetic semiconductor NixFe1-xCr2S4 (X = 0.985, 0,97, 0.96) has b een investigated over the temperature range from 12 to 600 K using a M ossbauer technique. The electronic structure of Fe ions in NiCr2S4 Was calCUlated with the Hamiltonian incorporating free-ion term, axial an d rhombic crystal field, spin-orbital couplings, and exchange interact ions. The ground orbital state is separated by 9.64 \lambda\ from the first excited state, thereby making the quadrupole splitting somewhat insensitive to temperature. Using x-ray crystallographic data, the con tribution of direct lattice sum to the electric-field gradient has bee n considered. In calculating the temperature dependence of quadrupole splitting, the axial field parameter DELTA1 = -3.0\lambda\, the rhombi c field parameter DELTA2 = - 2.8 \lambda\, and the covalency factor al pha2 = 0.73 in Ni0.985Fe0.015Cr2S4 were determined. Magnetic hyperfine and quadrupole interactions in the antiferromagnetic state of Ni0.96F e0.04Cr2S4 at 12 K have been studied, yielding the following results: H = 147.8 kOe, 1/2e2qQ(1 + 1/3eta2)1/2 = -1.96 mm/s, theta = 66-degree s, phi = 90-degrees, and eta = 1.0. The line broadening which suggests the electron relaxation was observed with decreasing temperature.