Abstract
An experiment was carried out to investigate the effect of Al2O3 substitution, molar ratio n {=Fe3+/(Co2++Ni2++Al3+)}, concentration of alkali, and inflowed time of alkali on the magnetic and physical properties of Co-Ni-Al system spinel ferrite fine particles prepared 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(Al2O3)0.5x·n/2(Fe2O3), where x varied between 0 and 0.5 and n varied between 1.75 and 2.25. The typical magnetic properties were saturation magnetization σs=54.5×10−6 Wb·m/kg, residual magnetization σr=28.9×10−6 Wb·m/kg, coercivity HcJ =531.6 kA/m. To remove the superparamagnetic substance, the coprecipitation fine particles were etched with dilute sulfuric acid. As a result, in the (CoO)0.5(NiO)0.4(Al2O3)0.01·(Fe2O3) composition, when the excess NaOH and inflowed time were 0.5 mol and 1 s, respectively, the following magnetic and physical properties were obtained: σs=75.5×10−6 Wb·m/kg, σr=57.1×10−6 Wb·m/kg, HcJ=939.8 kA/m, K1=16.0×104 J/m3, K2=−6.3×104 J/m3, and HA=3.20 MA/m.
