Ferrimagnetic resonance and low temperature transition in Ni- and Co-substituted powder magnetite

Abstract

The effects of nickel and cobalt substitution on ferrimagnetic resonance in high-purity magnetite powder have been investigated. The low-temperature transition temperature and damping parameter, α, are found to decrease with increasing solute additions. The linewidth, ΔH, varies in proportion to the anisotropy field of the ferrites, narrowing with increasing nickel content but broadening with increasing cobalt content. Theg factor increases with the dopant concentration, passing through a maximum around room temperature. Decreasing the deviation from stoichiometry by appropriate annealing decreases the transition temperature shift but slightly increases ΔH, g and α.