Magnetic Tunability of Permalloy Artificial Spin Ice Structures

Abstract

This paper reports tunable ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ artificial spin ice structures of various geometrical lattice arrangements as a function of film thickness. We achieve the magnetic tunability by three distinct methods namely, geometrical arrangements of nanomagnetic elements in the form of square, kagome, and triangular lattices with the variation in film thickness (20, 30, and 50 nm) for each geometry and the applied field orientations. Magnetic force microscopy reveals that the nanoelements are in single-domain states, obeying the spin ice rules for the 20-nm-thick spin ice structures. A combination of nanoelements in single-domain and vortex states is observed with the increase in thickness up to 30 nm. For the 50-nm-thick elements, vortex and flux closure states are in evidence. Broadband ferromagnetic resonance spectroscopy establishes the presence of distinct resonant modes that are spatially localized in the nanomagnets of different orientations and, hence, can be controlled by the applied field orientations. The role of shape anisotropy on the static and dynamic properties is investigated systematically and complemented by extensive micromagnetic simulations. The results show great potential towards designing reconfigurable magnonic crystals for microwave filter applications.