MOSSBAUER STUDY OF SEVERAL FERRIMAGNETIC SPINELS

The ferrimagnetic spinels Fe3O4, NiFe2O4, CoFe2O4, MnFe2O4, and MgFe2O4 have been prepared and studied with the Mössbauer-effect technique over a wide temperature range both with and without large applied magnetic fields. The cation distributions have been determined and compared with magnetization measurements. For CoFe2O4 and MgFe2O4, this distribution depends on the heat treatment; two extremes-quenched and slowly cooled samples-have been investigated. The hyperfine magnetic fields at Fe57 nuclei in A and B sites have been obtained as a function of temperature. A number of hyperfine fields are identified with the B sites of CoFe2O4, MnFe2O4, and MgFe2O4 and attributed to the kind and distributions of cations in the nearest-neighbor A sites. From the data, the ratio of the Co(A)-Fe(B) and Mn(A)-Fe(B) to the Fe(A)-Fe(B) superexchange interactions is found to be 0.68 and 0.66, respectively. Since the Mössbauer spectra provides no evidence for Fe2+ ions in MnFe2O4, a canted spin arrangement for the Mn ions in A and B sites is proposed to account for the small observed magnetization. © 1969 The American Physical Society.