A Domain-Boundary Model for a High Coercive Force Material

Abstract

The coercive force of aligned Co₅ (rare earth) powders, while always much less than 2K/M, varies greatly with magnetizing field, even up to 50 kOe. The remanence is much more nearly constant. The coherent rotation model for noninteracting particles is not adequate to describe this behavior. A model is presented based on the idea that domain boundaries may be present and move easily, but that a sufficiently large field will drive them out so that they must be renucleated. Two experimental findings support this model. First, the measured rotational hysteresis integral value depends on whether or not a large field is applied before each measurement, as the model predicts. Second, magnetization jumps corresponding to nucleation have been directly observed in single particles. Calculations of the behavior of aggregates based on this single‐particle model show the type of variation of coercive force and remanence that has been observed.