Preparation and Moessbauer spectra of CoV2O4 spinel doped with Fe2+ on tetrahedral sites

Co2+sub(0.98)Fe2+sub(0.02)Fe3+sub(x)V3+sub(2-x)O4 (x approximately = 0.001) was obtained from a sample containing the iron dope mainly in the trivalent state, by reducing it at 9100C in a CO2/CO atmosphere. Moessbauer spectra of 57Fe at the tetrahedral site were taken between 5 and 300 K. Below the Curie temperature (143 K) there is a magnetically induced electric field gradient eQVsub(zz) and a reduction of the hyperfine field Hsub(hf). Values at 5 K are Hsub(hf) = 141 kG and eQVsub(zz) = 5.74 mm/s. The effective splitting of the Fe2+5E ground-state doublet, as estimated from the temperature dependence of eQVsub(zz) and Hsub(hf), is 2qdelta/k = 28 K. It is concluded that in these oxides the coupling of the electronic 5E states to local Jahn-Teller active E-modes of vibration is stronger than in comparable sulphides. (author)