Surface-Roughness-Induced Demagnetizing Fields in Thin Films and Their Influence Upon the Approach to Saturation

Abstract

The magnetic field generated by the magnetization has been calculated for films with rough surfaces. At large magnetic fieldstrengths the film is uniformly magnetized. Simple formulas for the demagnetizing factors are given, which are applicable provided that the inclination of the local film surface relative to the mean surface is not too large. A rough estimate of the demagnetizing factor for a direction in the plane of the film is given by π〈p2〉/λd. Here 〈p2〉 is the mean-square (linear) deviation of the actual film surface from the mean surface, λ the predominant wavelength of the surface roughness, and d the film thickness. A relatively small surface roughness, if distributed anisotropically, is sufficient to induce a significant uniaxial magnetic anisotropy. If the magnetic fieldstrength is only moderately high, the surface roughness gives rise to misalignment of the magnetization vector near the surface relative to the mean magnetization vector. The effect of this misalignment upon the average magnetization has been calculated by a method that takes account of the dipole-dipole interaction. The hard-axis magnetization curves calculated for films with anisotropic surface roughness are compared with those expected for films having uniaxial (bulk) anisotropy. Depending upon the degree of anisotropy of the surface roughness the two types of curves can be either very similar or quite different.