Brillouin light scattering by magnetic surface waves in dot-structured permalloy layers

Brillouin light scattering was used to investigate the magnetic properties of periodic arrays of square dots of permalloy obtained by electron beam lithography and ion beam sputtering from evaporated films. The frequencies of the magnetostatic surface waves were studied for square 2 mu m x 2 mu m dots of thickness 30 nm separated by intervals of 1 mu m and the results were compared to those obtained from the unpatterned permalloy film. The spin wave frequencies were found to be sensitive to the size: of the dots and to the direction of the applied field; at first view, the size dependence is reasonably interpreted to derive from the demagnetizing field effect. However, a closer inspection of the dependence of the frequencies versus the angle of incidence seems to show step-like variations, suggesting that the involved in-plane wave-vector could be locked and show quantized values related to the finite dimensions of the dots. Consequently, the simple model, based on the Damon-Eshbach expression modified by the demagnetizing field, appears to be insufficient, and the full description of the magnetic surface wave properties has to take into account their lateral confinement.