8Jakubovics J P. Magnetism and magnetic materials[M]. The In- stitute of Metals, London: 1987.
9Hessien M M, Rashad M M, Hassan M S, et al. Synthesis and magnetic properties of strontium hexaferrite from celestite ore [J]. Journal of Alloys ~ Compounds, 2009, 476(1/2)1373.