Structure and magnetic properties of FeAl₂O₄ synthesized by microwave magnetic field irradiation

The structure and magnetic properties of FeAl2O4 synthesized by microwave magnetic field (H-field) irradiation were investigated to reveal the effect of the H-field on the crystal structure and the magnetic characteristics of an antiferromagnetic material. The role of the H-field was investigated using a single-mode cavity, which can spatially separate the maximum points of the alternating electric field (E-field) and H-field in the cavity. In H-field irradiation, the crystallite diameter decreased compared to that in conventional heating. In conventional heating, the crystallite diameter did not change with increasing quenching speed. Thus, it is suggested that a decrease in crystallite diameter occurs during H-field irradiation. Furthermore, magnetization after H-field irradiation was greater than that after conventional heating. It is considered that magnetic clusters appear when Fe3+ partially replaces Al3+ in the octahedral sites in the grain boundaries, which were formed as a result of decreasing crystallite diameter.