Exploring the phases of 3D artificial spin ice: From Coulomb phase to magnetic monopole crystal

TL;DR

This study explores the phase diagram of 3D artificial spin ice with a diamond lattice, revealing various monopole crystal phases and how surface energetics influence the magnetic configurations.

Contribution

It provides the first detailed exploration of the phase diagram of 3D artificial spin ice, identifying multiple monopole crystal phases and the effects of surface energetics on magnetic states.

Findings

Identified a rich phase diagram including double and single monopole crystals and Coulomb phase.

Observed ferromagnetic stripe formation due to broken symmetry in demagnetised systems.

Demonstrated that surface energetics can tune the ground state of 3D artificial spin ice.

Abstract

Artificial spin-ices consist of lithographic arrays of single-domain magnetic nanowires organised into frustrated lattices. These geometries are usually two-dimensional, allowing a direct exploration of physics associated with frustration, topology and emergence. Recently, three-dimensional geometries have been realised, in which transport of emergent monopoles can be directly visualised upon the surface. Here we carry out an exploration of the three-dimensional artificial spin-ice phase diagram, whereby dipoles are placed within a diamond-bond lattice geometry. We find a rich phase diagram, consisting of a double-charged monopole crystal, a single-charged monopole crystal and conventional spin-ice with pinch points associated with a Coulomb phase. In our experimental demagnetised systems, broken symmetry forces formation of ferromagnetic stripes upon the surface, a configuration that forbids the formation of the lower energy double-charged monopole crystal. Instead, we observe crystallites of single magnetic charge, superimposed upon an ice background. The crystallites are found to form due to the intricate distribution of magnetic charge around a three-dimensional nanostructured vertex, which locally favours monopole formation. Our work suggests that engineered surface energetics can be used to tune the ground state of experimental three-dimensional ASI systems.