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Magnetic anisotropies of La–Co substituted M-type Sr hexaferrites studied by 57Fe Mössbauer spectroscopy with external magnetic fields

Magnetoplumbite-(M)-type hexaferrites are the most widely used base materials of permanent magnets. La–Co substitution in these M-type Sr hexaferrites improves these magnetic anisotropies. By 57 Fe Mossbauer spectroscopy using the single-crystalline samples, we have investigated the Fe electronic states in the La–Co substituted M-type Sr hexaferrites, Sr 1 − x La x Fe 12 − y Co y O 19, as a function of an external magnetic field to discuss the enhancement of these magnetic anisotropies. All observed 57 Fe Mossbauer spectra were well analyzed using the five subspectra corresponding to the five crystallographic nonequivalent Fe sites. At one site of these five Fe sites, the 2 a Fe site, the extracted hyperfine interaction parameters clearly show the Co substitution and external magnetic field dependences, revealing the increments of the 3 d electrons in the Fe ions, which are caused by the substitution of Co 2 + ions for Fe 3 + ions at the neighbor 4 f 1 Fe site. This hybridization between the Fe ions and the Co ions induces the non-negligible unquenched orbital momentum in the Fe ions at the 2 a Fe site. Our findings represent an enhancement of the magnetic anisotropies in Sr 1 − x La x Fe 12 − y Co y O 19.