Multiplets of collective spin wave modes during magnetization reversal in a one dimensional magnonic crystal consisting of alternating-width nano stripes

We have studied the field evolution of spin waves frequency in a dense array of dipolarly interacting magnetic stripes of alternating widths during themagnetization reversal process by Brillouin light scattering technique. This represents a model system of a one-dimensional magnonic crystal which can sustain collective spin excitations. Their frequencies have been accounted for by a simple analytical approach when all the stripes are in the coaligned magnetization state. Each excitation of the array observed in the magnetically saturated state splits into either a doublet or a triplet in the field range where the inversion of the stripe magnetization takes place. This has been interpreted as due to the simultaneous presence, within the probed region, of clusters of adjacent stripes with either parallel or antiparallel magnetization.