Rare earth substitutions in M-type ferrites

In hexaferrites of the composition SrFe12O19 (SrM), Sir was substituted by R = La, Sm, and Nd. The precursors were weighed according to different Sm3+/Sr2+ ratios (n = Sm3+/Sr2+), where n was varied between 1/16 and 1/2. The samples were produced by hydrothermal synthesis. The effects of the rare earth substitution on the magnetic properties were investigated, measuring magnetization and magnetocrystalline anisotropy but also applying Mossbauer spectroscopy and nonmagnetic resonance. Nd and Sm substitution increases the intrinsic coercivity without causing any significant deterioration in either the saturation magnetization or the remanence, whereas La substitution has only a small effect on the intrinsic coercivity of SrM.