Effect of Co stearate addition on magnetic properties of anisotropic SrFe/sub 2/ W-type ferrite magnets

We investigated the effect of Co stearate as a new reducing agent, with SiO/sub 2/ and CaO additives, on the magnetic and physical properties of SrFe/sub 2/ W-type hexagonal ferrite. We found that the magnetic properties of SrO/spl middot/8.5Fe/sub 2/O/sub 3/ were considerably improved by adding 0.3 wt% of Co stearate, 0.3 wt% of SiO/sub 2/, and 0.7 wt% of CaO simultaneously. The optimum condition for preparing magnets were as follows: chemical analysis composition, Sr/sup 2+//sub 0.973/Si/sup 4+//sub 0.088/Ca/sup 2+//sub 0.166/Co/sup 2+//sub /0/sub .008/Fe/sup 2+//sub 1.581/Fe/sup 3+//sub 16.064/O/sub 27/; semisintering condition, 1350/spl deg/C/spl times/4.0 h in nitrogen gas atmosphere; drying condition, 200/spl deg/C/spl times/0.5 h in air; sintering condition, 1160/spl deg/C/spl times/1.5 h in nitrogen gas atmosphere. The resulting magnetic and physical properties were J/sub m/=0.48 T, J/sub r/=0.44 T, H/sub cJ/=189.0 kA/m, H/sub cB/=178.8 kA/m, (BH)/sub max/=34.7 kJ/m/sup 3/, T/sub c/=493/spl deg/C, and n/sub B/=28.8/spl mu//sub B/. The temperature dependences of J/sub m/, H/sub cJ/, and K/sub A/ were measured in these samples; K/sub A/ and H/sub A/ were 3.10/spl times/10/sup 5/ J/m/sup 3/ and 1303 kA/m at 20/spl deg/C, respectively. The temperature dependence of K/sub A/ and H/sub A/ was similar to that in M-type hexagonal ferrite.