Preparation and Mössbauer spectra of CoV 2O 4 spinel doped with Fe 2+ on tetrahedral sites

Abstract

Co 2+ 0.98Fe 2+ 0.02Fe 3+ ϵ V 3+ 2- ϵ 04 ( ϵ ⋍ 0.001) was obtained from a sample containing the iron dope mainly in the trivalent state, by reducing it at 910°C in a CO 2/CO atmosphere. Mössbauer 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 eQV zz and a reduction of the hyperfine field H hf. Values at 5 K are H hf=141 kG and eQV zz=5.74 mm/s. The effective splitting of the Fe 2+ 5E ground-state doublet, as estimated from the temperature dependence of eQV zz and H hf, is 2q δ/k = 28 K . It is derived 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.