An interpretation of an empirical formula for the coercivity of polycrystalline iron

Abstract

It was previously found that thre was a simple empirical relationship between the average of certain measurements on spike-like magnetic domains observed on (110) surfaces of crystals in iron and silicon-iron and the coercive field of the samples. An approximate formula was calculated for the field strength required to cause such domains to expand irreversibly, and it was found to be similar to, but not in close agreement with the empirical formula for the coercive field. The similarity was sufficient to suggest that the shapes of the hysteresis loops of the specimens were mainly governed in the region of the coercive field by this irreversible expansion, rather than by the domain wall impedance effects which one would expect to predominate in magnetically harder materials. A more detailed theoretical analysis now shows that the field strength at which irreversible expansion of the `spikes' occurs is quite close to the coercive field as obtained from the empirical formula.