Ferromagnetic resonance frequency of a thin Mo-permalloy film

Abstract

There is great interest both in the magnetic recording and wireless phone industries in the development of magnetic films with permeabilities that reach out into the GHz frequencies. In order to obtain such films the understanding of the frequency response of the ferromagnetic resonance of basic materials is needed. In this study the permeability of a thin film of Mo permalloy is measured up to 3 GHz utilizing a strip loop device. The effect of an externally applied field (Hdc) along the easy axis and hard axis on the transverse bias permeability as a function of frequency is measured through resonance. The full width at half maximum (Δf ) of the imaginary part of the permeability at resonance which is related to resonance damping is also measured. It is found that in the vicinity of Hdc-Hk near zero, Δf increases with decreasing dc field. This phenomenon is explained in terms of the Hoffmann ripple theory.