Magnetic properties of Co/(CoNi)Fe2O4 nanocomposite magnet powders

Co/(CoNi)Fe₂O₄ nanocomposite powders were prepared by mixing coprecipitated (CoO)_0.9(NiO)_0.1·Fe₂O₃ nanoparticles with Co nanoparticles, which were synthesized by alcohol reduction. TEM observations reveal that the powder consists of Co and (CoO)_0.9(NiO)_0.1·Fe₂O₃ nanoparticles with an average particle size of 30-50 nm. While the coercivity (H_cJ) is 156 kA/m, the saturation magnetization (σ_s) of 115.8 Am²/kg is obtained, which is comparable to that of Co nanoparticles. In the hysteresis loop, magnetization changes smoothly with field as the hysteresis behavior of a single-phase material. The high recoil ratio (R_recoil) of 0.69 and the positive ΔM values suggest the presence of the exchange coupling between Co and (CoNi)Fe₂O₄ nanoparticles.