Uniaxial films with square hard-direction loops

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Abstract
Certain uniaxial permalloy films are found to exhibit extremely square hard-direction hysteresis loops. Faraday-effect observations reveal wall motion when fields are applied in this direction. It is also clearly seen that these effects are due to the breaking up of the film into fine domains running parallel to the easy direction, but the density of Néel walls appears too low to explain the observed remanence. The occurrence of such films is related to the size of the anisotropy dispersion, which was found to vary rather rapidly with evaporation rate around 400 Å min-1. A number of structural studies suggest that the relevant effect of this is to give a high density of impurities.