Influence of cobalt substitution on the magnetocrystalline anisotropy of X-type hexaferrites Sr₂Co_xFe_30-xO₄₆

We investigate the composition dependence of the magnetic properties in X-type hexaferrites Sr2CoxFe30-xO46. We prepared single crystals including various contents of cobalt ions using a flux method. The samples with x >= 1.58 exhibited a different behavior in the [21 (1) over bar(1) over bar0] and [01 (1) over bar0] directions at 100 K, which was observed by magnetic measurements and Lorentz transmission electron microscopy. Such anisotropy was not observed in the sample that included slightly less cobalt ions (x=1.32). In contrast, the Curie temperature was independent of the cobalt content. It was concluded that such strong magnetocrystalline anisotropy was caused by the cobalt ions especially at low temperature.