Magnetic Tunability of Permalloy Artificial Spin Ice Structures

Abstract

Artificial spin ice (ASI) structures, consisting of arrays of interacting, single domain nanomagnets (NMs) are promising model systems to explore microscopic features of geometrical frustration [1]. While the structural geometry is responsible for tuning the shape anisotropy and the configurational anisotropy of the system, the strength of dipolar coupling can be modified by the film thickness. In the present work, we achieved magnetic tunability for Ni80Fe20 (Py) ASI structures by three distinct methods namely, the geometrical arrangements of the nanomagnets, the variation in film thickness (20 nm, 30 nm and 50 nm) for each geometry and the applied field orientation [2]. The different ASI geometries such as square spin ice (SSI), kagome spin ice (KSI) and comparatively newer triangular spin ice (TSI) structures are shown in Fig. 1 (a), (b) and (c) respectively. The corresponding hysteresis loops in Fig. 1 (d) depict a marked difference in magnetization reversal mechanism with the variation in film thickness which indicates a possible transition from single domain nanostructure to the formation of vortex states with increasing thickness. The ferromagnetic resonance (FMR) spectra, shown in Fig. 2 explain the dependence of various spin wave modes and their spatial localization on the structural symmetry, film thickness and applied field (Happ) orientation. Micromagnetic simulations are in good agreement with the experimental data and shows the space-frequency resolved localization of the spin wave modes. The results show a great potential towards designing reconfigurable magnonic crystals for microwave filter applications.