Study of nanocrystalline thin cobalt films with perpendicular magnetic anisotropy obtained by thermal evaporation

Abstract

We have performed a detailed investigation of the morphological and magnetic domain structures of nanocrystalline thin cobalt films with perpendicular magnetic anisotropy. The films were thermally evaporated at an incidence angle of 0° in a vacuum of about 10−5mbar and possessed thicknesses in the range from 60nm to 100nm. The films were studied by X-ray photoelectron spectroscopy (XPS), electron diffraction of transmission electron microscopy (TEM), atomic force microscopy (AFM), magnetic force microscopy (MFM) and the Fresnel mode of TEM. The films are polycrystalline and consist of very densely packed grains with sizes at the nanometer range. The grains are roundish in shape and generally exhibit no geometric alignment. The films are mainly composed of the hexagonal close-packed (HCP) phase of cobalt and possess preferential orientation of the cobalt grains with the hexagonal axis perpendicular to the film surface. 70nm thick films and thicker have fully perpendicular magnetization, while 60nm thick films possess clearly dominating perpendicular magnetization component. The magnetic domain structure is in the form of stripe domains forming a maze pattern. When the film thickness increases from 60nm to 100nm, the average grain size increases from 28.9nm to 31.5nm and the average domain width increases from 79.4nm to 98.7nm.