Self-focusing of spin waves in Permalloy microstripes

Excitation and propagation of spin waves in Permalloy microstripes magnetized in their plane perpendicularly to the axis have been investigated by means of microfocus Brillouin light scattering spectroscopy with high spatial resolution. We show that the spatial profile of the spin-wave beam demonstrates a focusing at a certain distance from the excitation source depending on the stripe width. A model connecting the observed phenomenon with an interference of different spin-wave modes existing in the stripe due to the finite-size effect is proposed.