ACTIVATION VOLUMES OF REVERSAL IN ULTRAFINE PARTICLES AND RECORDING MEDIA

Theoretical studies have been made of the fluctuation field Hf of a fine particle system with randomly oriented easy axes. The variation of Hf with applied has a minimum close to the coercive force. Experimental data for a system of weakly interacting fine cobalt particles give reasonable quantitative agreement with the theory. Experimental data on tape particles show a more complex variation. The activation volume associated with magnetisation reversal, which can be calculated from Hf is much smaller than the particle volume. This, in conjunction with the form of the variation of Hf with field may be related the magnetisation reversal mechanism. © 1990.