Observation of ferromagnetic resonance in the time domain

Optical pump-probe spectroscopy has been used to observe damped ferromagnetic resonance (FMR) oscillations in thin film Fe samples. The FMR was pumped by magnetic field pulses generated by an optically triggered photoconductive switch, and probed by means of time resolved measurements of the magneto-optical Kerr rotation. The photoconductive switch structure consisted of a parallel wire transmission line, of 125 mu m track width and separation, defined on a semi-insulating GaAs substrate. The biased transmission line was optically gated at one end so that a current pulse propagated along the transmission line to where the sample had been overlaid. The magnetic field associated with the current pulse is spatially nonuniform. By focusing the probe beam on the sample at different points above the transmission line the effect of the orientation of the pump field has been studied. The gyroscopic motion of the magnetization has been modeled by solving the Landau-Lifshitz-Gilbert equation and the magneto-optical response of the sample has been calculated by taking account of both the longitudinal and polar Kerr effects. The calculated and measured magneto-optical Kerr rotations are found to be in reasonable agreement. (C) 1999 American Institute of Physics. [S0021-8979(99)78608-1].