Magnetism of Submicroscopical Iron Particles

The magnetic fields around submicroscopical iron particles were tested with iron oxide colloid in an electron microscope. The colloid particles usually spread evenly by diffusion. Magnetic fields of several hundred oersteds are required to concentrate the colloid particles visibly at certain spots. We found colloid around iron particles concentrated to various degrees. The colloid was attracted less by smaller particles. The smallest particles did not attract any colloid. The particles were measured and grouped into three following categories: (a) Particles with strong, all around colloid attraction, indicating many domains. Stem volume of the dendritic particles much bigger than 109 A3, (b) Particles with colloid attractions at spots, indicating one or a few domains. (c) Particles without colloid attraction, indicating no well-developed domains. Stem volume much less than 109 A3.