Abstract
An experiment was carried out to investigate the effect of Cr substitution on the magnetic and physical properties of Co-Ni spinel ferrite fine particles by the chemical coprecipitation method without post annealing. The chemical coprecipitation compositions were chosen according to the formula (CoO)0.5(NiO)0.5−x(Cr2O3)0.5x·n/2(Fe2O3), where x varied between 0 and 0.2, and n between 2.0 and 2.5. Good magnetic properties were achieved with materials of composition (CoO)0.5(NiO)0.35(Cr2O3)0.075·(Fe2O3). The typical magnetic properties were saturation magnetization σs=33.9×10−6 Wb·m/kg, coercivity HcJ=549.3 kA/m, K1=7.6×104 J/m3, K2=−36×104 J/m3, and anisotropy field HA=5.57 MA/m. Furthermore, the particles were tried to etch in the diluted sulfuric acid solution (concentration 0.5∼2.0%, etching time 6∼30 h) for the purpose of removing super paramagnetic fine particles. Good magnetic properties were achieved with materials of concentration 1.5% and etching time 24h. The typical magnetic properties were σs=91.99×10−6 Wb·m/kg, HcJ=1.39 MA/m, K1=22.8×105 J/m3, and K2=−128.6×105 J/m3. The value of HA can not measured because a measurement magnetic field was not enough.
