Influence of the deviation from stoichiometry on the magnetic properties of Zn-rich NiZn ferrites

The influence of the deviation from stoichiometry on the magnetic properties has been investigated on the compositions given by the formula (NiO)α(ZnO)1-α(Fe2O3)xwhere α = 0.30 ; 0.36 and 0.9 < x < 1.1. The authors describe all the cares needed to prepare such compositions and the tests used before succeeding in obtaining magnetic property values which are characteristic and comparable. The influence of the deviation from stoichiometry upon the initial susceptibility is important near the Curie temperature and over a fairly large temperature range ;it decreases at low temperatures. This influence is also spectacular on the ceramic parameters of the materials (grain growth, density). Concerning other properties, crystallographic (lattice constant) or magnetic (Ms, Tc), the influence of the deviation is much lower but unambiguous. It is the variation of the Curie temperature with x which is responsible for the large susceptibility variations (previously mentionned by other authors at room temperature). The variation of Tccould be related to the variation of the lattice constant with x.