Variations in Anisotropy Magnitude and Magnetization Direction in Planar Films under Equilibrium Conditions

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Abstract
NiFe films were studied using an rf probe technique to map remanent magnetization direction and local Hk values over the surface. Two probe sizes were used with tip diameters of 0.8 and 0.25 mm. The film area coupled is smaller than the tip size in each case so that the small probe could resolve parameter differences less than 0.1 mm apart. The inhomogeneity in a 1×1‐mm square remote from any film edges, (determined by means of 100 measurements uniformly taken on a rectangular grid) was compared with that measured for the entire film. Results indicate that for the 27 films studied values of Hk with a range and frequency consistent with that implied by a Δ90 measurement are very nearly randomly distributed over the entire surface. Deviations from a random distribution occur near edges or other film features which contribute shape anisotropy. Remanent magnetization direction, in contrast, is almost entirely determined by the demagnetizing fields of film features so that directions in the 1×1‐mm area do not represent a random sample from a parent distribution taken from the entire film. These data do not support the conclusion that easy axis angle variations in such local areas (remote from edges, etc.) may be greater than that implied by an α90 measurement as suggested by Dove and Long.