Investigations on Barium Ferrite Magnets

Abstract

Barium ferrite (BaO:6Fe₂O₃) has been investigated magnetically to test the predictions of fine particle theory in the region of grain sizes larger than the critical one for which no satisfactory theory exists as yet. Grain size and coercive force of polycrystalline magnets (nonoriented and crystal oriented) were closely related to sintering temperatures. A comparison of theoretical and observed temperature dependence of coercive force is made and shows a close fit when certain reasonable assumptions are made. Susceptibilities showed values attributed to rotation of the magnetization vector for samples of high coercive force only (4000 oe), while wall movements contribute more or less to the susceptibility of all other samples. Domain patterns show wall movements in applied fields on samples with particle thickness down to 10×10⁻⁴ cm. Patterns on grains below 5×10⁻⁴ cm thickness (_IH_C more than 2000 oe) indicate reversals of magnetization by the rotation process. On magnets of the transition particle size both processes can be observed side by side, the walls being less movable for higher coercive forces.