Nonlinear Behavior of Ferromagnetic Thin Films

Abstract

The authors report a study of the behavior of Permalloy thin films at high microwave signals. The cases where films are polarized either parallel or perpendicular to the film plane are successively investigated at X and V bands. With a parallel polarization, the absorption via a first-order process can be present at X band either as a subsidiary absorption or as a premature decline of the main resonance, depending on the film thickness. At V band, only a subsidiary absorption was expected; it was effectively observed in some films with a large critical field (≃45 Oe). With perpendicular polarization, new experimental observations (such as an important main resonance shifting, a large variation of the linewidth at low level, a saturation of the uniform mode via a second order process, and a foldover effect leading to relaxation oscillations) at X and V bands were made and explained. Finally, with a strong interaction between films and electromagnetic waves having thus been shown, possible applications such as power limiters are indicated.