Cobalt doped γ-Fe ₂ O ₃ nanoparticles: Synthesis and magnetic properties

We demonstrate here the wet chemical synthesis of cobalt doped γ-Fe ₂ O ₃ nanoparticles and the subsequent effect on magnetic properties with the variation in dopant concentration. It is observed that cobalt can be homogeneously doped into the γ-Fe ₂ O ₃ lattice up to 5 mol% without any appreciable change in the particle size (∼6 nm). Further increase in cobalt concentration (10 mol% here) resulted in an increase in particle size (∼9 nm) due to possible adsorption of a cobalt layer on the surface of γ-Fe ₂ O ₃ nanoparticles rather than complete doping in the iron oxide lattice. The ac susceptibility measurements revealed an increase in blocking temperature (T _B ) with percentage variation in cobalt doping (2-10%), indicating substitution of Fe ³⁺ ions by Co ²⁺ ions in the γ-Fe ₂ O ₃ lattice. The dc magnetization measurements showed an increase in saturation magnetization only up to 5%, beyond which it significantly diminished. The reduction in saturation magnetization is attributed to the contribution from surface anisotropy in cobalt coated γ-Fe ₂ O ₃ nanoparticles.