Observation and control of collective spin-wave mode hybridization in chevron arrays and in square, staircase, and brickwork artificial spin ices

T Dion,W R Branford,J C Gartside,A Vanstone,H Kurebayashi,D M Arroo,K D Stenning

doi:10.1103/physrevresearch.4.013107

Abstract

Dipolar magnon-magnon coupling has long been predicted in nanopatterned artificial spin systems. However, observation of such phenomena and related collective spin-wave signatures have until recently proved elusive or been limited to low-power edge modes which are difficult to measure experimentally. Here we describe the requisite conditions for dipolar mode-hybridization, how it may be controlled, why it was not observed earlier, and how strong coupling may occur between nanomagnet bulk modes. We experimentally investigate four nanopatterned artificial spin system geometries: chevron arrays, square, staircase, and brickwork artificial spin ices. We observe significant dynamic dipolar-coupling in all systems with relative coupling strengths and avoided-crossing gaps supported by micromagnetic-simulation results. We demonstrate reconfigurable mode-hybridization regimes in each system via microstate control, and in doing so elucidate the underlying dynamics governing dynamic dipolar-coupling with implications across reconfigurable magnonics. We demonstrate that confinement of the bulk modes via edge effects plays a critical role in dipolar hybridized modes, and treating each nanoisland as a coherently precessing macro-spin or a standing spin-wave is insufficient to capture experimentally observed coupling phenomena. Finally, we present a parameter-space search detailing how coupling strength may be tuned via nanofabrication dimensions and material properties.

Highlights

Artificial spin ices (ASIs) are arrays of magnetically frustrated nanoislands with vast low-energy state degeneracy [1,2,3,4]
We demonstrate reconfigurable modehybridization regimes in each system via microstate control, and in doing so elucidate the underlying dynamics governing dynamic dipolar-coupling with implications across reconfigurable magnonics
We know from studies on synthetic antiferromagnets [35,36,45,46] and bistable 1D nanoisland arrays [21,23,25] that hybridizedmodes are distinguished by in-plane dynamic magnetization moving in-phase or out-of-phase termed acoustic and optical respectively as illustrated in Figs. 1(c) and 1(d)

Summary

INTRODUCTION

Artificial spin ices (ASIs) are arrays of magnetically frustrated nanoislands with vast low-energy state degeneracy [1,2,3,4]. The dipolar-interaction responsible for coupling in nanopatterned RMCs offers relative freedom and reconfigurability of mode-hybridization phenomena [15]. We previously investigated width-modified bicomponent square ASI, alternating rows of thin and wide nanoislands along each sublattice, termed staircase ASI. This provides access to type-3 states consisting of three-in, one-out vertex configuration whose spin-wave signature had yet been measured. Applying field 45◦ to sublattice axes, we observed an avoided crossing due to antiparallel magnetization This geometry with perpendicular state preparation and measurement field directions is atypical, and its use and efficacy in exploring mode-hybridization is further investigated here. Experimental, fitting, and simulation methods are all found in the Supplemental Material [44]

Acoustic and optical spin waves

Mode hybridization in two-nanoisland arrays

Mode hybridization in ASIs

Mode profiles

Tailoring coupling via geometry

CONCLUSION