Relaxation pathways and emergence of domains in square artificial spin ice

TL;DR

This study uses kinetic Monte Carlo simulations to explore how different models of nanomagnet switching barriers influence the formation of diverse domain structures in square artificial spin ice, revealing the importance of intrinsic barrier contributions.

Contribution

It demonstrates that incorporating chiral barrier splitting and state-dependent local torques in models leads to more realistic domain morphologies in artificial spin ice.

Findings

Mean-field barrier models produce string avalanches.

Chiral barrier splitting enables coral domain formation.

Intrinsic barrier effects influence mesoscale domain emergence.

Abstract

Multi-domain states of square artificial spin ice show a range of different morphologies ranging from simple stripe-like domains to more organically shaped coral domains. To model the relevant dynamics leading to the emergence of such diverse domain structures, simplified descriptions of the switching behavior of individual nanomagnets are necessary. In this work, we employ kinetic Monte Carlo simulations of the demagnetization of square artificial spin ice toward its ground state, and compare how the choice of transition barriers affect the emergence of mesoscale domains. We find that the commonly used mean-field barrier model (informed by equilibrium energetics only) results in propagation of ground-state string avalanches. In contrast, taking into account chiral barrier splitting enabled by state-dependent local torques supports the emergence of complex-shaped coral domains and their successful relaxation towards the ground state in later relaxation stages. Our results highlight that intrinsic contributions to switching barriers, in addition to the effect of extrinsic defects often attributed to nanofabrication irregularities, can subtly shift favored transition pathways and result in different emergent mesoscale features. Future kinetic Monte Carlo models that describe the evolution of artificial spin systems should thus account for these effects.