Mossbauer investigation of Sr-Fe-O hexaferrites with La-Co addition

Summary form only given. The magnetic properties of anisotropic M-type SrFe/sub 12/O/sub 19/ ferrites can be improved by La and Co addition. First, La/sup 3+/ substitutes for Sr/sup 2+/ and, second, most of the Co/sup 2+/ is substituted for Fe/sup 3+/ in the octahedral 4f/sub 2/ sites. A valence change of some Fe/sup 3+/ to Fe/sup 2+/ in the 2a site has also been evidenced. With the aim of relating the location of Co/sup 2+/ in the crystal structure of the M-type ferrite to the intrinsic magnetic properties, we performed a Mossbauer investigation in the 77-550 K temperature range of Sr/sub 1-x/La/sub x/Fe/sub 12-x/Co/sub x/O/sub 19/ powders with x=0 to 0.4. The presence of secondary phases was avoided by applying a special process, consisting of a double calcination at high temperature (1260/spl deg/C) with an intermediate milling. The phase composition of the samples was checked by X-ray diffraction.