Experimental and theoretical study of quantized spin-wave modes in micrometer-size permalloy wires - art. no. 134429

Using Brillouin light scattering measurements, we have studied the properti es of the spin waves in various arrays of Permalloy wires showing widths of 0.5, 1, and 1.5 mum. When the transferred in-plane wave vector kappa (para llel to), specified by the experimental setup, is perpendicular to the wire s, a sampling of the Damon-Eshbach surface mode branch giving rise to a set of discrete dispersionless modes is observed. We attribute this behavior t o a lateral quantization of the wave vector q(parallel to) of the magnetic excitations. The frequency separation between two adjacent modes is found t o decrease when the width D of the wires increases. However, this frequency dependence does not simply follow the expected one assuming the usual naiv e relation q(parallel to ,n) = n pi /D, which would not allow one to give a ccount of the behavior of the lowest mode n = 0. We have performed numerica l calculations of the dynamical magnetization response functions of these r ectangular cross section wires using the method of finite elements. The mag netic parameters used in these calculations were derived from the experimen tal Brillouin spectra of the unpatterned films. Both our experiments and ou r calculations agree with the results expected from the unpatterned film as suming the following discrete values: q(parallel to ,0) = 0, q(parallel to ,n) = pi (n + beta)/D. The zero value observed for the lowest mode n = 0 si mply results from the calculation and does not need for an additional hypot hesis as previously proposed.