Kerr Effect and Bitter Pattern Measurements of Easy-Axis Distributions in Uniaxial Permalloy Films

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Abstract
Measurements on small regions (1 mil2) of magnetic films have been made with a Kerr magneto‐optic apparatus that utilizes a laser light source and employs narrow‐band detection techniques. Sensitivity is adequate to allow observations on permeabilities, remanent flux, and other properties. At the same time, Bitter patterns may be obtained facilitating detailed correlation between dynamic magnetic behavior and remanent state domain patterns. Bitter patterns have been recorded during the course of an angular distribution fall‐back experiment. The pictures have been assembled sequentially as a motion picture showing the remanent domain state developed throughout the experiment. Dynamic Kerr effect observations show that significant domain wall rearrangements occur near zero transverse field. The direction of M in small regions of single domain films has been determined to 0.1° using an MH alignment technique, and hence an alternative estimate of the angular distribution of easy axes is obtained. Strong transverse magnetostatic coupling between regions is of importance in both the fall‐back and MH alignment measurements. The validity of various easy axis distribution measurements is discussed in the light of present observations.