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

Highly Al3+ ion doped nanocrystalline SrFe12−xAlxO19 (0≤x≤12), were prepared by the auto-combustion method and heat treated in air at 1100°C for 12h. 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 Al3+ doping, the lattice parameters decrease due to smaller Al3+ ion replacing Fe3+ ions. Morphological analysis performed using transmission electron microscope show growth of needle shaped ferrites with high aspect ratio at Al3+ ion content exceeding x≥2. Al3+ substitution modifies saturation magnetization (MS) and coercivity (HC). The room temperature MS values continuously reduced while HC value increased to a maximum value of 18,100Oe at x=4, which is an unprecedented increase (∼321%) in the coercivity as compared to pure Sr-Ferrite. However, at higher Al3+ content x>4, 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. ► The study reports synthesis and characterization of highly aluminum doped SrFe12−xAlxO19 ferrite.► Synthesis of pure phase aluminum doped Sr-Ferrite using autocombustion method is reported. ► An unprecedented increase in coercivity ∼321% is observed upon aluminum at x=4 Al doping. ► The observed magnetic properties of SrFe12−xAlxO19 are related to changes in anisotropy. ► And morphology in compound upon aluminum doping.