Production and Magnetic Properties of Co- and La–Y-Doped Strontium Ferrite

Abstract

In  this  study,  rare  earth-substituted  M-type  Sr-hexaferrites  with  the  chemical  compositions  Sr_1-x(RE)_xFe_12-xCo_xO₁₉ and Sr_1-2x(RE)_2xFe_12-xCo_xO₁₉ were prepared using the solid-state reaction method. All of the hexaferrite samples were characterized using instrumental techniques of X-ray diffraction, optical microscopy, and vibrating sample magnetometer to study the effect of La–Y substitution on the structural and magnetic properties. The bulk densities changed from 4.45 to 4.96 g/cm³ after sintering at 1250°C. X-ray  diffraction  diagrams  of  all  the  sintered  samples  confirmed that the Sr-hexaferrite phase persisted with La/Y and Co co-substitution without secondary phases. However, the substitution affected the peak intensities and the positions of Bragg angles. The reduction in the saturation magnetization (M_s) was observed from 25.4 emu/g for single La to 9.40 emu/g for La–Y substitution. It was found that the coercivity (H_c) improved from 502 to 2080 Oe for a single Y-substituted sample and a single La-substituted sample, respectively. The measured squareness ratio (M_r/M_s) was larger than 0.5, indicating that the change in the magnetization can be realized by the rotation. The results suggest that the incorporation of rare-earth cations can improve the magnetic properties of strontium hexaferrites.