Stress Effects in Evaporated Permalloy Films

The magnetic properties of evaporated Permalloy films subject to external uniform stresses were experimentally determined and the resulting changes in magnitude and direction of HK were compared to recently reported theories. In general, qualitative agreement between the data and theory was found when the angular dispersion resulting from the stress was small. When the stress induced dispersion was large the discrepancies between data and theory become quite large. Some of the discrepancy in HK may be due to instrumental difficulties in measuring HK under conditions of large angular dispersion. The variation of HC with stress follows that of HK, but in a much less sensitive manner. When HK exhibited a minimum, HC showed a corresponding minimum while the dispersion and the hard axis coercivity had corresponding maxima. The stress-induced interchange of the easy and hard axes was found to proceed partially through a rotation of axes and not by just the anisotropy decrease predicted by theory. The axis rotation under these conditions is due to the excessive angular dispersion, the nonuniform nature of films, and the slight differences between the effects of tension and compression.