The Effects of Hydrogen Reduction on Magnetic Properties of Barium Ferrite Particles

Abstract
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 reduced-substituted Ba-ferrite particles are reoxidized, the coercivity is reversible in the first step but irreversible in the second step. During the third step, the magneto-plumbite structure was collapsed with formation of α-Fe and BaFeO_s-x phases and consequently the coercivity distribution was broad and the coercivity irreversible. The coercivity and saturation magnetization decreases and increases up to 130 emu/g respectively. In this study, it is found that the substituted cations 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 coercivity before the collapse of magneto-plumbite structure is attributed to the migration of substituted cations in hexagonal Ba-ferrite structure.