Magnetic anisotropies in cobalt-nickel ferrites (NixCo 1-xFe2O4)

Abstract

This work presents a detailed study on the various magnetic anisotropics of NixCo1-xFe2O4 prepared by using a mechanochemical process. The results indicated that the magnetic anisotropy of NixCo1-xFe2O4 was strongly correlated with the Co5+ concentration. The Ni2+ substitution readily led to a decrease in the magnetocrystalline anisotropy and coercivity. While a large uniaxial anisotropy was induced in CoFe 2O4 by magneto-annealing, the uniaxial anisotropy decreased with the Ni concentration in NixCo1-xFe 2O4 and disappeared in the pure NiFe2O 4. A short-time mechanical milling was found to significantly increase the coercivity in NixCo1-xFe2O 4 samples and high coercivities of 5.1 kOe and 2.8 kOe were achieved in the CoFe2O4 and the Ni0.5Co 0.5Fe2O4 samples respectively. The microstructure and magnetic studies indicated that the milling-induced high coercivity could be ascribed to milling-induced stress anisotropy and to the pinning effects of defects.