CRYSTALLOGRAPHIC AND MAGNETIC-PROPERTIES OF COXFE1-XCR2S4

Abstract

The mixed series CoxFe1-xCr2S4 has been studied by x-ray, Mossbauer spectroscopy, and superconducting quantum-interference device (SQUID) magnetometry. The crystal structure is found to be a cubic spinel, and the lattice constant a0 decreases linearly with increasing cobalt concentration. Mossbauer spectra of CoxFe1-xCr2S4 have been taken at various temperatures ranging from 4.2 to 300 K. The iron ions are ferrous and occupy the tetrahedral sites. The Curie temperature increases linearly with cobalt concentration, suggesting that the superexchange interaction for the Co-S-Cr link is stronger than that for the Fe-S-Cr link. Magnetic hyperfine and quadrupole interactions in Co0.9Fe0.1Cr2S4 at 4.2 K have been studied, yielding the following results: H(hf) = 80.8 kOe, 1/2e2qQ(1 + 1/3eta2)1/2 = 2.65 mm/s, theta = 15-degrees, phi = 75-degrees, and eta = 1.O. It is notable that, as the temperature decreases below the Curie temperature, quadrupole splitting increases with decreasing temperature, suggesting the presence of an electric field gradient and accompanying relaxation effects. Magnetic susceptibility measurements by SQUID magnetometry show that superexchange interactions between Fe2+ ions are ferrimagnetic.