Mössbauer studies of the lithium ferrite-aluminate system

Abstract

Mössbauer studies of the series Li 0·5Fe 2·5− a Al a O 4 where ‘ a’ has values from 0 to 2.5 have been carried out. It is observed that in addition to the six line nuclear Zeeman spectrum, a doublet also appears at the centre and the intensity of this doublet increases with the increasing aluminium content. As a consequence of magnetic dilution, some iron species are isolated from the other magnetic species and have a short range of magnetic order. This results in varying sizes of magnetic clusters; the regions which as a whole have very little magnetic interaction with the surroundings but within which there can be any type of magnetic ordering. The relaxation rate is much faster in the smaller clusters (also referred to in literature as superparamagnetic clusters) and give rise to paramagnetic spectrum. An attempt has been made to find the relative number of iron species which give rise to paramagnetic spectrum in terms of the surrounding non-magnetic neighbours. The anomalous magnetisation behaviour of this series of compounds and the temperature dependence of the hyperfine magnetic fields at the two sites has been discussed.