A study of Pr-substituted strontium hexaferrite by hydrothermal synthesis

The possibility of replacing Sr by La and Fe by Co and the subsequent improvement of the magnetic properties of the M-type ferrite stimulated our interest in studying other rare-earth ion substitutions. We have found that Sm and Nd substitutions can increase the coercivity of the hydrothermally synthesised Sr hexaferrite powder without causing any significant fall in the saturation magnetisation. In the present work, Pr-substituted Sr hexaferrite particles were prepared by hydrothermal synthesis and subsequent calcinations. The effects of the initial Pr/Sr ratio and the calcination temperature on the structure, particle morphology and magnetic properties of Pr-substituted Sr hexaferrite were investigated by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. It was found that, under hydrothermal conditions, the Pr3+ additives did not substitute exclusively into the SrM structure but this could be achieved to a greater extent by subsequent calcinations at high temperatures. Compared to the effect of Sm, Nd and La substitutions, Pr improves the coercivity by 14%, which is only smaller than that of Sm substitution but higher than those of Nd and La substitution. Pr substitution increases the coercivity without causing any significant deterioration in either the magnetisation or the remanence.