Optical pump-probe studies of the rise and damping of ferromagnetic resonance oscillations in a thin Fe film

Small-amplitude ferromagnetic resonance (FMR) oscillations have been studie d in a thin Fe film by means of an optical pump-probe technique in which th e sample magnetisation is pumped by an optically triggered magnetic field p ulse and probed by means of the magneto-optical Kerr effect. The magnetic f ield pulse is generated by a current pulse in a coplanar transmission line on which the sample is overlaid. The sample was probed at different positio ns above the transmission line, to study the effect of pump fields applied at different angles to the sample plane, and the static field was applied i n different directions relative to the plane of incidence. The Landau-Lifsh itz-Gilbert equation has been used to model the response of the sample magn etisation and the experimental and theoretical curves are found to be in re asonable agreement. From the phase and decay of the FMR oscillations the ri se time of the pump field inside the sample and the value of the Gilbert da mping constant have been determined. The rise time of the pumping field wit hin the sample is found to depend upon the orientation of the pumping held relative to the plane of the sample. The value of the damping constant is f ound to depend upon the orientation of the static field relative to the tra nsmission line. We suggest that the observed behaviour results from the gen eration of eddy currents. (C) 2000 Elsevier Science B.V. All rights reserve d.