Colloquium: Artificial spin ice: Designing and imaging magnetic frustration

TL;DR

This paper reviews the development of artificial spin ice systems, which are engineered magnetic nanostructures that mimic natural frustrated magnetic materials, enabling direct observation and control of magnetic frustration phenomena.

Contribution

It provides a comprehensive overview of recent experimental and theoretical advances in designing, imaging, and understanding artificial spin ice, highlighting new insights into magnetic frustration and monopole excitations.

Findings

Artificial spin ice mimics natural frustrated magnetic systems.

Experimental control and imaging of individual nanostructures.

Observation of magnetic monopole-like excitations.

Abstract

Frustration in the presence of competing interactions is ubiquitous in the physical sciences and is a source of degeneracy and disorder, giving rise to new and interesting physical phenomena. Perhaps nowhere does it occur more simply than in correlated spin systems, where it has been studied in the most detail. In the past few years, a new perspective has opened in the study of frustration through the creation of artificial frustrated magnetic systems. These materials consist of arrays of lithographically fabricated single-domain ferromagnetic nanostructures that behave like giant Ising spins. The nanostructures' interactions can be controlled through appropriate choices of their geometric properties and arrangement on a (frustrated) lattice. The degrees of freedom of the material can not only be directly tuned, but also individually observed. Experimental studies have unearthed intriguing connections to the out-of-equilibrium physics of disordered systems and non-thermal granular materials, while revealing strong analogies to (spin) ice materials and their fractionalized magnetic monopole excitations, lending the enterprise a distinctly interdisciplinary flavor. The experimental results have also been closely coupled to theoretical and computational analyses, facilitated by connections to classic models of frustrated magnetism, whose hitherto unobserved aspects have here found an experimental realization. We review the considerable experimental and theoretical progress in this field, including connections to other frustrated phenomena, and we outline future vistas for progress in this rapidly expanding field.