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 degrees C 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 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 (M-S) and coercivity (H-C). The room temperature M-S values continuously reduced while Tic value increased to a maximum value of 18,100 Oe at x=4, which is an unprecedented increase (similar to 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. Published by Elsevier B.V.