Ferromagnetic resonance in three-fold nano-ellipse clusters

We have experimentally and theoretically characterized ferromagnetic resonance (FMR) in 120°-symmetric clusters formed from three closely-spaced but non-contacting permalloy nano-ellipses together with the angular and thickness dependence. To achieve maximum sensitivity and coupling, we fabricate well separated arrays of such clusters on a coplanar waveguide. The arrays were patterned using electron-beam lithography, and deposited using electron-beam evaporation. Theoretical simulations were performed using the dynamical matrix method and show excellent agreement with the experimental results. We find that the overall response of the clusters is dominated by, and can be represented as a superposition of, the spectra arising from the individual macrospins. This finding has important implications for using FMR to unravel the spectra of more complex structures, such as spin ice lattices formed by assembling elemental building blocks into arrays.