The structure–property relationships in M-type hexaferrites: Hyperfine interactions and bulk magnetic properties

57Fe Mössbauer spectroscopic measurements have been made at 296 K on single crystals of MFe12O19 (M=Ba, Sr, Pb) oriented parallel and perpendicular to the c axis, permitting the establishment of the systematics of the static and dynamical aspects of the hyperfine interactions, and their relationship to crystal/chemical structures for the five Fe3+ sublattices, and to the bulk magnetic properties. With the exception of the electric quadrupole interaction at the 2b site, and the dependence of the 2b intensity on the crystal orientation, the magnitude of the hyperfine interactions of a given Fe3+ site exhibits only small variations among the different hexaferrites. The magnitude of the quadrupole interaction at the 2b site varies by more than 10%, with the 2b site in PbFe12O19 exhibiting the smallest value. The relative intensity of the 2b subspectrum varies markedly among the three hexaferrites for observations parallel and perpendicular to the c axis. Although all display the expected anisotropy resulting from the libration of the 2b Fe3+ parallel to the c axis, the anisotropy is considerably larger for PbFe12O19 than for BaFe12O19 or SrFe12O19. It is remarkable that the bulk magnetic anisotropy follows the same order as the anisotropy in the dynamical displacement and crystalline electric field of the 2b site.

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