We have experimentally and numerically investigated the dispersion of collective spin waves propagating through arrays of longitudinally magnetized nanowires (NWs) with a periodically modulated width. Two nanowire arrays with single-side modulation and different periodicities of modulation were studied and compared to the nanowires with a homogeneous width. The spin-wave dispersion, measured up to the third Brillouin zone of the reciprocal space, revealed the presence of two dispersive modes for the width-modulated NWs, whose amplitude of the magnonic band depends on the modulation periodicity, and a set of nondispersive modes at higher frequency. These findings are different from those observed in homogeneous width NWs where only the lowest mode exhibits sizeable dispersion. The measured spin-wave dispersion has been satisfactorily reproduced by means of the dynamical matrix method. The results presented in this work are important in view of the possible realization of tunable frequency magnonic devices

We report the electrical detection of multiple ferromagnetic (FM) resonance modes in multilayers of Pt/Fe20Ni80/Ru/Fe20Ni80 using microwave spin pumping and the inverse spin Hall effect (ISHE) as a function of Ru layer thickness tRu. The electrically detected voltage signals were analyzed for the anti-parallel magnetization state as well as the “spin-flop” magnetization state of the two Fe20Ni80 layers. When the two FM layers are antiferromagnetically (AFM) coupled (tRu = 1 nm), both the optic and acoustic modes were observed. The amplitude of the acoustic mode voltage signals obtained increases with frequency. However, when the two magnetic layers are ferromagnetically coupled (tRu = 1.4 nm), only acoustic mode was observed whose voltage signals decreases as frequency increases. We demonstrate the tunability of the sign of the ISHE voltage in the AFM coupled system by controlling the polarization of the spin currents.

The magnetization reversal and dynamic behaviors of Ni80Fe20 nanowires (NWs) with controlled periodic width modulation on single and double sides of the wires have been systematically investigated using magneto-optical Kerr effect and broadband ferromagnetic resonance spectroscopy. In contrast with the single resonance mode observed in the homogeneous NWs, the NWs with periodic width modulation display two distinct resonance modes (the fundamental mode at lower frequency and the high frequency mode which is localized in the modulated regions) due to the non-uniform demagnetizing field. An enhancement of the coercive field is observed for the width modulated NWs when compared with homogeneous NWs. We also observed that the high frequency mode and the frequency difference between the two distinct modes are very sensitive to the modulation profile and film thickness. The results obtained from our experimental results agree well with the micromagnetic simulations. The results have potential implications in the design of tunable magnonic filters.

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 tunable relative displacement () of the notches sequence on the two lateral sides. Both symmetric (=0) and asymmetric (= 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 deriving from the splitting of the modes characteristics of the nanowire with homogeneous width. Interestingly, the amplitude of the magnonic band, the frequency difference of the doublet as well as their relative scattering intensity can be efficiently controlled by increasing  rather than having single-or symmetric (=0) double-side widthmodulation.

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