Magnetic anisotropy in ferromagnetic thin films

Abstract

Measurements of the induced magnetic anisotropy in thin iron and nickel films were performed by means of the magnetoresistance effect (MRE) in three perpendicular directions, at 120°K and 300°K. Two kinds of induced anisotropies were detected. The first one is independent of the magnetic field H d , which was applied during the deposition of the film. It is related in both materials to an angle of incidence effect, arising from the geometry of the deposition. This anisotropy in thin iron films has a radial symmetry in the plane of the film, and decreases to zero with the growing thickness of the film. In nickel films the same kind of anisotropy was found to exist in a wide range of thicknesses, increasing with the growth of the film, but having a circular symmetry. The second anisotropy, detectable in relatively thick iron films (5000 Å), is aligned with its easy magnetic axis parallel to the field H d . Its magnitude was found to be about 0.1 K 1 at 120°K (K 1 is the first cubic magnetocrystalline anisotropy constant for iron) and decreased at room temperature. The MRE in the transverse-perpendicular direction points to the presence of a preferred orientation described by plane (111) as contact plane with the substrate, and by the [11 2 ] direction in this plane parallel to H d . This preferred orientation also accounts for the magnitude, direction and temperature dependence of the field induced anisotropy. This interpretation is based on a magneto-elastic interaction due to magnetostriction and isotropic tensile stresses in the plane of the film.