Temperature dependence of spontaneous magnetization of ultrafine Fe particles in Fe-SiO2 granular solids

Abstract

We have studied the temperature dependence of the spontaneous magnetization of ultrafine Fe particles by measuring the initial susceptibility χ∼M2s (T)/kBT in the superparamagnetic state. It was found that Bloch’s law Ms=M0(1−BT3/2) gives good description at temperatures much higher than the blocking temperature of the Fe particles. The value B is substantially larger than that of the bulk Fe, due to magnetic surface effect and finite size effect. Size distribution and magnetostatic interaction between particles have also been studied.