Nonlinear magneto-optic measurement of flux propagation dynamics in thin Permalloy films

Time-resolved nonlinear optics are used to study the propagation of magnetic flux pulses in a 250 nm Permalloy film. The flux is generated in the film by coupling it to a coplanar waveguide structure driven with broadband voltage pulses. Flux pulses propagated in the film with a phase velocity of 4.2×105 m/s and a group velocity of 1.5×105 m/s. Both velocities are consistent with the predictions of Damon–Eshbach theory for magnetostatic surface waves with 200–300 μm wavelengths. Within 100 μm of the excitation source, flux pulses decayed monotonically but with no measurable delay.