Local modifications for tuneable artificial spin ice

Despite many attempts to design new correlated systems to influence the properties of a physical system, it is often those inspired by nature that yield the best results. Artificial spin ices (ASI) are 2D projections of geometrically frustrated materials, comprised of lithographically defined macrospins, which are often used to experimentally model more complex atomistic systems. In addition, ASI exhibit collective dynamic behavior and emergent monopole stabilization that can be applied to probabilistic computing, signal propagation, and logic devices. The capacity to design an almost infinite number of topologies have made ASI an exciting candidate for novel computation.

Defects can have bountiful effects on the local physical properties of crystal systems and may be used to tune their properties. In this talk, novel ASI systems are presented that have been designed to influence the collective dynamic behavior of the macrospins in the array by introducing local modifications to the lattice. The first system introduces the quasi-hexagonal ASI lattice, which exhibits an induced shape anisotropy from introducing parallel islands along one symmetry axis. This enables multimodal frustration in the lattice across different sites as well as symmetry breaking during the breakdown of macrospins at high magnetic fields. The second system presented is a Kagome lattice with a magnetic defect, which acts as a source of emergent monopoles at lower energy-barriers than in the pristine lattice. Recent results of the delicate interplay between defect and lattice states are studied in the context of signal propagation applications by magnetic imaging techniques and micromagnetic modelling. This system shows that it is possible to manipulate the defect-induced monopoles whilst minimizing parasitic nucleation events in the lattice bulk. The outlook and directions for locally modified ASI devices will be reviewed in the wider landscape of ASI applications.