Determination of Magnetic Imperfections in Thin Films

Abstract

By means of a selective ferromagnetic resonance technique, we have succeeded in determining the spatial distribution of the magnetic properties of thin magnetic films. In contrast to other types of diagnostic techniques, the method determines the relevant local magnetic parameters of the sample directly. This is accomplished by sequentially exposing small areas of the film to an rf magnetic field via an aperture in one of the walls of a microwave cavity. To obtain maximum resolution at a given apparatus sensitivity, the aperture wall is substituted by a vacuum‐deposited copper film on a dielectric substrate. To data, magnetic quantities such as anisotropy, exchange constant, linewidth, gyromagnetic ratio, magnetization, etc. of regions as small as 5 μ in diameter have been selectively examined. Since spatial variation of these quantities is due to imperfections in the material, results of our measurement exhibit the direct influence of these imperfections on the local magnetic properties of the film. For example, we have found that the effective magnetization decreases and linewidth increases substantially near a nonmagnetic imperfection, and also the existence of regions where the magnetic easy axis rotates gradually over π/2 rad, etc. Typical data on Permalloy films are presented along with a discussion of the theoretical and experimental aspects of the method.