The mixed series CoxFe1-xCr2S4 has been studied by x-ray, Mossbauer sp
ectroscopy, and superconducting quantum-interference device (SQUID) ma
gnetometry. The crystal structure is found to be a cubic spinel, and t
he lattice constant a0 decreases linearly with increasing cobalt conce
ntration. Mossbauer spectra of CoxFe1-xCr2S4 have been taken at variou
s temperatures ranging from 4.2 to 300 K. The iron ions are ferrous an
d occupy the tetrahedral sites. The Curie temperature increases linear
ly with cobalt concentration, suggesting that the superexchange intera
ction 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 decrea
ses below the Curie temperature, quadrupole splitting increases with d
ecreasing temperature, suggesting the presence of an electric field gr
adient and accompanying relaxation effects. Magnetic susceptibility me
asurements by SQUID magnetometry show that superexchange interactions
between Fe2+ ions are ferrimagnetic.