Magnetic phase transitions in substituted barium ferrites BaFe12−x(Ti0.5Co0.5)xO19 (x=0–5)

High temperature magnetic properties for a series of Ti, Co-substituted M-type barium hexaferrite BaFe12−x(Ti0.5Co0.5)xO19 (x=0–5) have been studied by measuring magnetization and magnetic susceptibility. BaFe12O19 (x=0) shows the hard magnetic property at room temperature in magnetization curve. The saturation magnetization Ms and the coersivity HC decrease with increasing Ti, Co composition x. Curie temperature TC shifts to lower temperature with x and becomes TC=491 K in the composition x=2.5. At this composition, another ferrimagnetic state was observed above TC; the ferrimagnetic to paramagnetic transition temperature locates at TC2=752 K. The second transition temperature TC2 has a maximum at around x=3 and becomes 703 K at x=5 where the low transition temperature locates at TC=219 K. In the high temperature ferrimagnetic phase, magnetization value is small compared to the low ferrimagnetic phase. Thus a canted or uncompensated antiferromagnetic structure produced by the Fe–Co and/or Co–Co exchange interaction can be considered.

► Magnetic measurements of BaFe12−x(Ti0.5Co0.5)xO19 (x=0 to 5) have been made.
► Ferromagnetic transition temperature TC decreases with x.
► Second ferrimagnetic phase having a small spontaneous magnetization was observed above TC at x=3–5.
► A canted or uncompensated antiferromagnetic structure can be considered in the second phase.