Magnetic properties of Co-Ni spinel ferrite fine particles with high coercivity prepared by the chemical coprecipitation method

We investigated the effect of NiO substitution on the magnetic and physical properties of Co ferrite prepared by the chemical coprecipitation method without postannealing. The chemical coprecipitation compositions were chosen according to the formula (CoO) _1-x(NiO)_x·n/2(Fe₂O₃), where x varied between 0 and 1.0 and n between 1.0 and 3.0. We found that the single-phase Co-Ni spinel ferrite fine particles could be prepared by the chemical coprecipitation method without postannealing. Optimum magnetic properties were achieved with materials of composition (CoO)_0.5(NiO)_0.5·1.125(Fe₂O ₃). The typical magnetic and physical properties are saturation magnetization σ_s = 56.3 × 10^-6 Wb · m/kg (44.8 emu/g), coercivity H_cJ = 506.9 kA/m (6.37 kOe), Curie temperature T_c = 557.3°C, the lattice constant a = 0.8384 nm, and the average particle size = 30 nm. The rotational hysteresis integral Rh, which is related to the magnetization mechanism of these fine particles, is 1.57. We found that the magnetization mechanism is an incoherent rotation one