Superparamagnetism in Magnetically Dilute Systems

Superparamagnetic behavior observed in magnetically dilute systems is discussed. The clusters that behave like superparamagnetic fine particles are ferromagnetic or ferrimagnetic regions separated magnetically from the matrix, because these regions are surrounded by nonmagnetic atoms. The magnetic properties of dilute oxide systems such as: 0.9 ZnFe2O4-0.1 NiFe2O4; 0.9 FeTiO3-0.1 Fe2O3; and Y1.5Ca1.5Fe4.5Sn1.5O12 are better understood if we take into account the existence of the superparamagnetic clusters. The Langevin function type magnetization curves observed for the Fe—Cr alloys in the composition range where ferromagnetism just disappears, however, were found not to have the characteristics of superparamagnetism, although superparamagnetic clusters are predicted by the localized model.