Effect of sodium addition on structural and magnetic properties of solid state processed SrFe12-xAlxO19 (x ≤ 4)

Aluminum-substituted M-type strontium hexaferrite (SrM-Al, SrFe12-xAlxO19, 0 <= x <= 4) with uniform microstructure and excellent magnetic properties was synthesized by conventional ceramic processing based on solid state reaction. Coercive field was highly enhanced by heavy doping with Al3+ although magnetization was significantly reduced. However, formation of coarse microstructure and poor development of H-c with low level doping of Al3+ disturbed practical application. To promote phase formation and to suppress growth of coarse grains which were induced by incorporation of Al3+ ions, SrM-Al ceramics was processed with NaOH. Such Na-assisted processing of SrM-Al reduced formation of non-magnetic phases and assisted development of uniform fine grains. In addition, the large residual strain by Al3+ doping was partially relieved by the same approach. As a result, saturation magnetization of SrFe12-xAlxO19 was remarkably enhanced and the BHmax of randomly oriented hard magnetic ceramics was improved to 1.23MGOe by concomitant addition of Na and Al ions.

Automated summary

The magnetic properties of aluminum-substituted M-type strontium hexaferrite were improved by NaOH-assisted processing, which promoted phase formation, suppressed formation of non-magnetic phases, developed uniform fine grains, and partially relieved the residual strain caused by aluminum doping.