THE EFFECTS OF HYDROGEN REDUCTION ON MAGNETIC-PROPERTIES OF BARIUM FERRITE PARTICLES

A reduction process of the substituted Ba-ferrite has been found to be devided into three steps. At the first and second steps, the magneto- plumbite structure maintains and the coercivity increases. When the re duced-substituted Ba-ferrite particles are reoxidized, the coercivity is reversible in the first step but irreversible in the second step. D uring the third step, the magneto-plumbite structure was collapsed wit h formation of alpha-Fre and BaFeO3-x phases and consequently the coer civity distribution was broad and the coercivity irreversible. The coe rcivity and saturation magnetization decreases and increases up to 130 emu/g respectively. In this study, it is found that the substituted c ations prevent the magneto-plumbite structure from collapse during the reduction process and furthermore migrate from the magnetic sites of 4f(IV)+2a, 2b, and 12k to 4f(VI) and 12k'. An increase in the coercivi ty before the collapse of magneto-plumbite structure is attributed to the migration of substituted cations in hexagonal Ba-ferrite structure .