Free Oscillations of the Magnetization in Permalloy Films

Free oscillations of the magnetization are excited in magnetic uniaxial Permalloy films by a small dc step pulse field with less than 0.35 nsec risetime. This field is applied perpendicularly to the magnetization and in the plane of the film. The resulting damped oscillations of the magnetization are detected by a sampling oscilloscope and investigated between 500 Mc and 1200 Mc. The eigenfrequency is determined by a dc field parallel to the magnetization and by the orientation of the easy axis. The eigenfrequencies agree reasonably with the ferromagnetic resonance frequencies of the same films. The damping constants $\lambda$ evaluated from the decay time of the free oscillations and from the linewidth of ferromagnetic resonance also agree fairly well and are in the range from 100 Mc to 300 Mc. The experimental results are analyzed by means of the Landau-Lifshitz equation.