The Dynamic Behaviour of Magnetic Thin Films†

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Abstract
The effective damping constant 𝛌eff is measured as a function of frequency by U.H.F. ferromagnetic resonance. The results are compared with those obtained by using a small angle free oscillations technique. In addition, both methods offer a means of determining the gyromagnetic ratio γ. The damping factor 𝛌eff is measured as a function of the anisotropy field Hk, and also of the composition of the nickel—iron film. A possible dispersion of 𝛌eff within the film is discussed. 𝛌eff is also deduced from the exponential decay times of the damped oscillations which occur in experimental hard direction switching waveforms. Such waveforms agree qualitatively with coherent rotational theory. Experimental switching waveforms obtained with large amplitude pulsed reversing fields, applied at 135° to the easy direction, also agree qualitatively with theoretical predictions. Small observed deviations from theory are, perhaps, related to local inhomogeneities of both the anisotropy field and the easy direction. For 135 switching with lower fields, the rotation is incoherent, probably on account of the same inhomogeneities. Switching threshold curves are measured, and these differ markedly from the theoretical astroid stability diagram, because of the disturbing influences of domain switching and incoherent rotation.