Artificial spin ices are arrays of correlated nano-scale magnetic islands that prove an excellent playground in which to study critical phenomena. In this contribution, we discuss how both geometry and the coupling of islands to external fields influence magnetic order. Using Lorentz transmission electron microscopy, we study a transition between antiferromagnetic and ferromagnetic order across a continuum of spin ice geometries. We show how emergent anisotropies can arise in field-driven processes and how relaxation timescales can be adjusted locally within arrays through a coupling to a site-specific bias field. Our work demonstrates artificial spin ice as an excellent testbed in which to probe non-equilibrium phenomena in low-dimensional systems.
We study, theoretically, omni-directional Euclidean transformation-optics (TO) devices comprising planar, light-ray-direction changing, imaging, interfaces. We initially studied such devices in the case when the interfaces are homogeneous, showing that very general transformations between physical and electromagnetic space are possible. We are now studying the case of inhomogeneous interfaces. This case is more complex to analyse, but the inhomogeneous interfaces include ideal thin lenses, which gives rise to the hope that it might be possible to construct practical omni-directional TO devices from lenses alone. Here we report on our progress in this direction.
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