Physical and magnetic properties of highly aluminum doped strontium ferrite nanoparticles prepared by auto-combustion route

Highly Al3þ ion doped nanocrystalline SrFe12 xAlxO19 (0rxr12), were prepared by the auto-combustion method and heat treated in air at 1100 1C for 12 h. The phase identification of the powders performed using x-ray diffraction show presence of high-purity hexaferrite phase and absence of any secondary phases. With Al3þ doping, the lattice parameters decrease due to smaller Al3þ ion replacing Fe3þ ions. Morphological analysis performed using transmission electron microscope show growth of needle shaped ferrites with high aspect ratio at Al3þ ion content exceeding xZ2. Al3þ substitution modifies saturation magnetization (MS) and coercivity (HC). The room temperature MS values continuously reduced while HC value increased to a maximum value of 18,100 Oe at x1⁄44, which is an unprecedented increase ( 321%) in the coercivity as compared to pure Sr-Ferrite. However, at higher Al3þ content x44, a decline in magnetization and coercivity has been observed. The magnetic results indicate that the best results for applications of this ferrite will be obtained with an iron deficiency in the stoichiometric formulation. Published by Elsevier B.V.