Observations of magnetization reversal in cobalt-rare-earth particles

A new technique for the separation of strongly magnetic powders by particle size has led to observations of discontinuous magnetization changes in samples of cobalt-rare-earth particles. These magnetization jumps were investigated in a single particle, and it was found that they occurred at various reproducible and strongly quantized fields, whose value depended on the value of the field previously applied to saturate the sample. This suggested that the coercive force of these materials might be very sensitive to the nature of the surface, which was verified experimentally. These results add support to the interpretation of the magnetic properties of high-crystal-anisotropy permanent magnet materials in terms of domain boundary nucleation and motion.