Abstract
In the emerging field of magnon-spintronics, spin waves are exploited to encode, carry and process information in materials with periodic modulation of their magnetic properties, named magnonic crystals. These enable the redesign of the spin wave dispersion, thanks to its dependence on the geometric and magnetic parameters, resulting in the appearance of allowed and forbidden band gaps for specific propagation directions. In this work, we analyze the spin waves band structure of two-dimensional magnonic crystals consisting of permalloy square antidot lattices with different geometrical parameters. We show that the frequency of the most intense spin-wave modes, measured by Brillouin light scattering, exhibits a universal dependence on the aspect ratio (thickness over width) of the effective nanowire enclosed between adjacent rows of holes. A similar dependence also applies to both the frequency position and the width of the main band gap of the fundamental (dispersive) mode at the edge of the first Brillouin zone. These experimental findings are successfully explained by calculations based on the plane-wave method. Therefore, a unified vision of the spin-waves characteristics in two-dimensional antidot lattices is provided, paving the way to the design of tailored nanoscale devices, such as tunable magnonic filters and phase-shifters, with predicted functionalities.
Highlights
D t w t/w two-dimensional (1-D and 2-D) yttrium iron garnet (YIG) films with an artificial micron-size periodicity and SWs generated by inductive methods[25]
In this work we exploit the Brillouin light scattering (BLS) technique to study the SWs spectrum of 2-D magnonic crystals (MCs) consisting of square antidot lattices (ADLs), i.e. arrays of holes drilled into a magnetic Permalloy film
By investigating the SWs dispersion characteristics of several square ADLs with different thickness (t) and inter-hole separation (w), we found that the frequency of the most relevant modes at Γ point, i.e. at the center of the Brillouin Zone (BZ), as well as the frequency position and the width of the band-gap at the BZ boundary (Y point, i.e. ky = π /a ) exhibit a universal dependence on the aspect ratio t/w of the ADL
Summary
D (nm) t (nm) w (nm) t/w two-dimensional (1-D and 2-D) yttrium iron garnet (YIG) films with an artificial micron-size periodicity and SWs generated by inductive methods[25]. YIG has the advantage of being a very low-damping material, but its integration into standard semiconductor technology is challenging due to the difficulties of growing and patterning high quality thin films on substrates different from gadolinium gallium garnet (GGG) single crystals Polycrystalline magnetic alloys such as NiFe (Permalloy) or CoFeB, would be better suited to meet to the industrial demand of miniaturization and integration, but their drawback is the relatively high SW damping which prevents propagation above a few microns. The experimental results are successfully interpreted on the basis of calculations performed by the plane wave method (PWM), taking into account both dipolar and exchange interactions[37] This general and unified view that governs the spin-wave characteristics in squared ADLs has not been previously identified, and offers useful information for predictive purposes and device design operating in the microwave frequency range
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