Al~(3+) doped M-type hexagonal Ba-Co ferrites synthesized via ball-milling assisted ceramic process: magnetism and its correlation with structural properties

摘要

Ba~(0.5)Co~(0.5)Al~( x )Fe~(12− x )O~(19)( x  = 0, 0.08, 0.16, and 0.24) hexaferrites are synthesized via ball-milling assisted ceramic process, and their crystal structure, microstructure, and magnetic properties were studied. The results show that all samples, calcined between 950 and 1150 °C, consist of the main M-type hexagonal Ba ferrite phase in combination of a small amount of CoFe~(2)O~(4)and Fe~(2)O~(3)phase. The lattice parameters of M-type hexagonal Ba~(0.5)Co~(0.5)Al~( x )Fe~(12− x )O~(19)decrease after Al_(3+)doping. The addition of Al_(3+)ions results in a reduction of crystallite size, which is attributed that the presence of foreign phase CoFe~(2)O~(4)and Fe~(2)O~(3)restrains the growth of the Ba~(0.5)Co~(0.5)Al~( x )Fe~(12− x )O~(19)crystallite. Magnetic characterization indicates that all samples exhibit hard magnetic properties. Trend of specific saturation magnetization of Ba~(0.5)Co~(0.5)Al~( x )Fe~(12− x )O~(19)sample, calcined at 1050 and 1150 °C, decreases with the increase in Al_(3+)content. The varied magnetic properties with substitution content ( x ) are well explained by the occupancy effects of Al_(3+)ions in magnetoplumbite structure. Ba~(0.5)Co~(0.5)Fe~(12)O~(19), calcined at 1150 °C, has the highest specific saturation magnetization value (56.07 emu/g), remanence (28.66 emu/g), and moment (10.76 µ ~(B)). Besides, with the increase of substitution content ( x ), magnetic domain type of ferrites, calcined at 1150 °C, changes from a single magnetic domain to a multi-domain type.