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

Thin permalloy films 10 nm and 60 nm thick were investigated. They were thermally evaporated at an incidence angle of 0° in a vacuum of about 10−5 mbar. 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 10–30 μm 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 10 nm thick, while in the films 60 nm thick the presence of cross-tie walls was only observed. The presence of cross-tie walls in the films 10 nm thick is reported for the first time. The coexistence of Néel type and cross-tie walls in the films 10 nm 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 30 nm in size; the films 60 nm thick had grains somewhat larger in size than the films 10 nm 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 10 μm scale.

► Thermally evaporated thin permalloy films 10 nm and 60 nm thick were investigated. ► The magnetic structure consisted of in-plane magnetized domains 10–30 μm in size. ► The domain walls of Néel type and cross-tie walls were observed. ► Cross-tie walls in the films 10 nm thick were observed for the first time. ► The morphological structure was composed of nanocrystalline grains.