Lorentz Microscopic Examinations of Polycrystalline Films with Biaxial Properties

Abstract

Polycrystalline Permalloy films with biaxial properties have been examined in detail by Lorentz microscopic techniques. The stable configuration for type I films, consisting of an array of discrete small squares, is a simple arrangement of four domains with complete flux closure and 90° walls along the diagonals. At high fields, a single domain configuration is obtained in which the spins along the edge deviate from the field direction due to the ``boundary anisotropy.'' The magnetization curling distances D along the edge are found to be proportional to MT/H, independent of the dimension of the square. The critical field HA for the flux closure structure is proportional to MT/L, where T is the film thickness. For type II films, composed of discrete thick squares superimposed on an isotropic continuous film, the conditions for flux closure are the same as for type I films. Type III continuous films with nonmagnetic square voids have also been examined, and their biaxial properties are similar to those of type II films.