Microwave effective linewidth in thin metal films

Abstract

An effective linewidth technique for characterizing microwave losses in thin ferromagnetic metal films, similar to the technique for ferrites, has been developed. The extension to metal films is nontrivial. A numerical solution of the electromagnetic boundary value problem for the fields inside the film must be used to evaluate the on- and off-resonance losses, and these calculated losses must be directly related to changes in the microwave cavity Q on an absolute scale. Specific measurements and analyses were done for polycrystalline permalloy on glass. Measurements at 10 GHz yield a change in 1/Q with field which is in accord with theory and can be modeled off resonance to obtain intrinsic losses. The analysis yielded an intrinsic Landau–Lifshitz damping parameter of 5.5×107 rad/s for permalloy. This corresponds to a half-power effective linewidth of 27 Oe, which is comparable to the best published 10 GHz linewidth for single-crystal iron films.