Appl. Phys. Lett. 105, 042409 (2014)

Credit: COURTESY OF VASSILIOS KAPAKLIS

Lithographically fabricated arrays of nanoscale magnets have garnered attention as mesoscopic realizations of spin ice, a state of magnetic order that shares deep similarities with the thermodynamic properties of water ice. In such 'artificial' spin ices, nanoislands act as giant spins that can point in one of two directions ('up' or 'down'). Importantly, the islands interact with each other through the dipolar interaction, and thus mimic the frustrated behaviour of naturally occurring spin ice materials. The Ising symmetry of the spins — that is to say, the fact they can only point in one of two opposite directions — is crucial for ensuring this analogy holds. However, real magnets may also possess spins with a greater degree of freedom: for example, in some cases they may be free to rotate in the plane, and are referred to as XY spins. Now, Unnar Arnalds and colleagues fabricate an array of disc-shaped islands that behave as XY-like superspins. These do not yet interact, but they do display thermal dynamics, by blocking and rotating freely at low and high temperature, respectively. More complicated artificial magnetic structures may therefore be just around the corner.