Ice-rule made manifold: phase transitions, topological defects and manifold restoration in two-dimensional artificial spin systems

TL;DR

This study explores how geometric modifications in two-dimensional artificial spin ices influence magnetic order, defect structures, and phase transitions, demonstrating tunable frustration and out-of-equilibrium dynamics in nano-magnetic arrays.

Contribution

It introduces a continuum of spin ice geometries controlled by island rotation, revealing tunable magnetic phases and defect types in artificial spin ices.

Findings

Ground state order changes from antiferromagnetic to ferromagnetic

Defects evolve from string-like to vortex-like structures

Geometry controls frustration and phase behavior

Abstract

Artificial spin ices are arrays of correlated nano-scale magnetic islands that prove an excellent playground in which to study the role of topology in critical phenomena. Here, we investigate a continuum of spin ice geometries, parameterised by rotation of the islands. In doing so, we morph from the classic square ice to the recently studied pinwheel geometry, with the rotation angle acting as a proxy for controlling inter-island interactions. We experimentally observe a change in ground state magnetic order from antiferromagnetic to ferromagnetic across this class of geometries using Lorentz transmission electron microscopy on thermally annealed cobalt arrays. The change in ordering leads to an apparent change in the nature of the defects supported: from one-dimensional strings in the antiferromagnetic phase to two-dimensional vortex-like structures in the ferromagnetic one, consistent with the scaling predicted by the Kibble-Zurek mechanism. Our results show how magnetic order in artificial spin ices can be tuned by changes in geometry so that a truly frustrated ice-rule phase is possible in two-dimensional systems. Furthermore, we demonstrate this system as a testbed to investigate out-of-equilibrium dynamics across phases.