Mechanochemically aided sintering process for the synthesis of barium ferrite: Effect of aluminum substitution on microstructure, magnetic properties and microwave absorption

This work reported a mechanochemically aided sintering process for the synthesis of BaFe12−xAlxO19 (x = 0.0, 0.5, 1.0, 1.5, 2.0) hexaferrite ceramic. A brief analysis was conducted on the synthesis mechanism of the pure barium ferrite, its morphology, and magnetic properties. By substitution of Al3+ ions into BaFe12O19 lattice, the size of the grains decreased and their hexagonal-plate shape tended toward a rod-like shape. These events led to a single domain nature in the grains and also an increase in their magneto-crystalline anisotropy. Single domain nature obtained a barrier against the movement of the domain walls, which led to an increase in coercivity. On the other hand, the increase of anisotropy led to the enhancement of coercivity, according to the Stoner-Wohlfarth model. The substitution of Al3+ ions also led to the decrease of the saturation magnetization, which was because of the lower magnetic moment of Al3+ ions (0 μB) compared to that of Fe3+ ions (+5 μB). As a result of substituting Al3+ ions with a value of x = 2, a maximum reflection loss of −43 dB was obtained at a frequency of 15.7 GHz.