Effect of Co stearate addition on magnetic properties of anisotropic SrFe2 W-type ferrite magnets

We investigated the effect of Co stearate as a new reducing agent, with SiO₂ and CaO additives, on the magnetic and physical properties of SrFe₂ W-type hexagonal ferrite. We found that the magnetic properties of SrO·8.5Fe₂O₃ were considerably improved by adding 0.3 wt% of Co stearate, 0.3 wt% of SiO₂, and 0.7 wt% of CaO simultaneously. The optimum condition for preparing magnets were as follows: chemical analysis composition, Sr²⁺_0.973Si⁴⁺_0.088Ca²⁺_0.166Co²⁺_{0.008Fe²⁺1.581Fe³⁺16.064O27; semisintering condition, 1350°C×4.0 h in nitrogen gas atmosphere; drying condition, 200°C×0.5 h in air; sintering condition, 1160°C×1.5 h in nitrogen gas atmosphere. The resulting magnetic and physical properties were Jm=0.48 T, Jr=0.44 T, HcJ=189.0 kA/m, HcB=178.8 kA/m, (BH)max=34.7 kJ/m³, Tc=493°C, and nB=28.8μB. The temperature dependences of Jm, HcJ, and KA were measured in these samples; KA and HA were 3.10×10⁵ J/m³ and 1303 kA/m at 20°C, respectively. The temperature dependence of KA and HA was similar to that in M-type hexagonal ferrite.}