Study of thermally evaporated thin permalloy films by the Fresnel mode of TEM and AFM

Abstract

Thin permalloy films 10nm and 60nm thick were investigated. They were thermally evaporated at an incidence angle of 0° in a vacuum of about 10−5mbar. The magnetic structure of the films was observed with the Fresnel mode of transmission electron microscopy (TEM), while their morphological structure was revealed using atomic force microscopy (AFM). The magnetic structure consisted of domains typically 10–30μm in size. The films were substantially magnetized in the plane of the film. The domain walls of Néel type as well as cross-tie walls occurred in the films 10nm thick, while in the films 60nm thick the presence of cross-tie walls was only observed. The presence of cross-tie walls in the films 10nm thick is reported for the first time. The coexistence of Néel type and cross-tie walls in the films 10nm thick means that their wall energies are comparable at this film thickness, and this statement is supported by the results of theoretical works. The morphological structure of the films was composed of nanocrystalline grains smaller than about 30nm in size; the films 60nm thick had grains somewhat larger in size than the films 10nm thick. The random distribution of the magnetocrystalline anisotropy of the individual nanocrystalline grains is found to be practically averaged out by exchange interaction, which leads consequently to the strongly reduced effective magnetic anisotropy and the wide magnetic domains on a 10μm scale.