Abstract
We calculate the magnetic anisotropy (MA) energy of W-type ferrites, Ba(Sr)Me2Fe16O27, where Me is Mg, Co, and Ni, using a cluster model and LS coupling on magnetic ions, along with the structural data obtained via x-ray and neutron diffractions. We show that the local MA energy of Fe3＋ and Me2+ on each non-equivalent site depends strongly on the local lattice structure around the magnetic ions. The bulk MA energy calculated for W-type ferrite with Me=Mg is found to be weakly dependent on the details of local lattice structures, and the calculated result is consistent with that observed for SrMg 2Fe16O27. Results for W-type ferrite with Me=Co suggest the appearance of a cone-type magnetic structure; however, c− plane MA may appear when a small amount of Co2+ resides on 12k sites. The finding could resolve the experimental controversy for the magnetic structure of W-type ferrite with Me=Co. Based on the results, we discuss site-selective substitution of Me2+ (Me = Fe, Co, and Ni) to enhance the performance of permanent magnets.
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