Dipole-Narrowed Inhomogeneously Broadened Lines in Ferromagnetic Thin Films

Abstract

An inhomogeneity in the magnetization of thin ferromagnetic films is shown to provide a mechanism for two-magnon scattering which contributes to the spin-wave resonance linewidth of thin ferromagnetic metal films. A normal (perpendicular) variation in the internal field has previously been assumed to explain the spinwave-resonance properties of thin films. In this work a planar variation in the magnetization is assumed which produces an inhomogeneously broadened linewidth. Since the inhomogeneity is much smaller than the average magnetization of the material, dipole forces will decrease the inhomogeneous broadening of the resonance line. Experimental results are in good agreement with the theory when eddy current losses are included and the inhomogeneity in the plane of the film is of the same order of magnitude as the normal inhomogeneity. As the film normal is rotated with respect to the magnetic field direction, the critical angle is approached at which the resonance conditions are the same throughout the film and the spins precess at a common frequency. At this angle the planar inhomogeneity will not be effective in broadening the excited mode. This effect is indicated in the data by a minimum in the frequency linewidth at this angle.