Magnetic and microstructural properties on Mn- and Ru-doped hexagonal barium ferrites

Magnetic and microstructural properties for Mn- and Ru-doped hexagonal barium ferrites have been investigated in terms of magnetization and scanning electron microscope (SEM) measurements. The field dependent magnetization data of BaFe/sub 12-x/Mn/sub x/O/sub 19/ (0 /spl les/ x /spl les/ 6), sintered at 1100/spl deg/C, reveal that with increasing the Mn concentration, the coercivity (H/sub c/) gradually increases whereas the saturated magnetization (M/sub s/) decreases. Remarkably, the H/sub c/ value at x = 6 is close to 1 tesla (T). Any noticeable difference in SEM images of the Mn-doped samples was not found, implying that the coercivity change in the Mn-doped ferrites is sensitive to the Mn content rather than the surface morphology. On the other hand, the Ru-doped BaFe/sub 8/Ru/sub 4/O/sub 19/ sample, in which the Ru ions are partially substituted into the Fe sites, did not show any substantial enhancement of H/sub c/. These substitution effects are presumably interpreted in terms of competing super-exchange interactions between magnetic ions in the nearest neighboring sites. The effect of grain size on coercivity and the magnetic coupling between the magnetic metal ions are discussed.