Spin wave dispersion and intensity correlation in width-modulated nanowire arrays: A Brillouin light scattering study

Using Brillouin light scattering spectroscopy and dynamical matrix method calculations, we study collective spin waves in dense arrays of periodically double-side width-modulated Permalloy nanowires. Width modulation is achieved by creating a sequence of triangular notches on the two parallel nanowire sides, with a periodicity of p = 1000 nm and a tunable relative displacement (Δ) of the notch sequence on the two lateral sides. Both symmetric (Δ = 0) and asymmetric (Δ = 250 and 500 nm) width-modulated nanowires were investigated. We have found that the detected modes have Bloch-type character and belong to a doublet derived from the splitting of the mode characteristics of the nanowire with the homogeneous width. Interestingly, the amplitude of the magnonic band, the frequency difference of the doublet, and their relative scattering intensity can be efficiently controlled by increasing Δ rather than having single- or symmetric (Δ = 0) double-side width-modulation.