Nature 500, 553–557 (2013)

Credit: © A. D. JEREZ ROMAN, I. GILBERT AND S. ZHANG

The concept of frustration is often invoked when describing systems that cannot reach a global energy minimum because of the presence of many energetically similar ground states. In magnetism, the topic has been the subject of intense investigation over the past decades, most notably when the origin of the frustration can be traced down to geometric constraints. Recently, these ideas have been revisited in lithographically fabricated arrays of interacting nanoscale magnets that, owing to their conceptual similarity with a celebrated frustrated magnetic system known as spin ice, are referred to as artificial spin ices. In principle, they represent an ideal platform for investigating magnetic frustration, but in practice they are often found to occur in frozen 'athermal' states, making the study of their equilibrium properties problematic. Peter Schiffer and colleagues now demonstrate a way to overcome this issue and bring artificial spin ices of different geometries into thermal equilibrium. Their annealing approach closely resembles a strategy for investigating the properties of these systems by numerical simulation, therefore making artificial spin ice even more attractive for studying frustrated magnetic materials.