Dynamic coupling and spin-wave dispersions in a magnetic hybrid system made of an artificial spin-ice structure and an extended NiFe underlayer

Abstract

We present a combined experimental and numerical study of the spin-wave dispersion in a NiFe artificial spin-ice (ASI) system consisting of an array of stadium-shaped nanoislands deposited on the top of a continuous NiFe film with non-magnetic spacer layers of varying thickness. The spin-wave dispersion, measured by wavevector resolved Brillouin light scattering spectroscopy in the Damon–Eshbach configuration, consists of a rich number of modes, with either stationary or propagating character. We find that the lowest frequency mode displays a bandwidth of ∼0.5 GHz, which is independent of the presence of the film underneath. On the contrary, the Brillouin light scattering intensity of some of the detected modes strongly depends on the presence of the extended thin-film underlayer. Micromagnetic simulations unveil the details of the dynamic coupling between the ASI lattice and film underlayer. Interestingly, the ASI lattice facilitates dynamics of the film either specific wavelengths or intensity modulation peculiar to the modes of the ASI elements imprinted in the film. Our results demonstrate that propagating spin waves can be modulated at the nanometer length scale by harnessing the dynamic mode coupling in the vertical, i.e., the out-of-plane direction of suitably designed magnonic structures.

A Brillouin light scattering study of the spin-wave magnetic field dependence in a magnetic hybrid system made of an artificial spin-ice structure and a film underlayer

“…As discussed in Ref. [13], the simulations suggest that modes (b,c,d) in Fig. 6 with frequencies close to one another contribute to peak (1).…”

“…The ASI lattice is formed by elongated nanoelements ("islands", in the following) to mimic the bistability of atomic spins in crystalline spin ice. The results presented here go beyond our previous work 13 , where the "dispersion curves" of spin waves at a particular field value were studied. We, here, address the question of how the eigenmodes evolve as a function of the externally applied field for a fixed wavevector.…”

“…The SW dynamics in the hybrid ASI/film systems at µ 0 H = 200 mT is reported in detail in Ref. [13], where it was found that the ASI modes with resonance frequencies below the DE mode of the uncoupled film are almost insensitive to the presence of the film underlayer: as found in the simulations, in this frequency range the modes show in the ASI layer a phase profile almost identical to that shown in Fig. 5 for the uncoupled ASI lattice, while in the film layer the dynamic magnetization is almost negligible.…”

“…The reconfiguration of the magnetic ordering can be driven by an external magnetic field stimulus, which in turn enables the manipulation of the spin-wave propagation characteristics, i.e., the peculiar profile of the spin-wave (SW) dynamics. The dynamics profile can be more or less uniform, confined in a restricted area of the primitive periodic cell 13 , or extended over a larger area. The specific dynamics of a spinwave mode determine the Brillouin light scattering (BLS) intensity, the mode bandwidth, and the group velocity 10,11,14,15 .…”

“…There has been significant progress in studies of the dynamics in two-dimensional lattices. More recently, studies have transitioned to the exploration of three-dimensional systems 16 such as magnetic multilayered systems and systems in which unpatterned films interface with patterned nanostructures (e.g., ASI) 13,17 . These studies address the question of how the vertical coupling can influence the in-plane spinwave propagation properties either through the static interaction (generating a non-uniform internal effective field distribution, B eff ) or the dynamic interaction (generating hybridized states between the magnetic oscillations in distinct layers).…”