Artificial Spin Ice

Geometrical frustration is known to significantly modify the properties of many materials. Pyrochlore spin ice and hexagonal water ice are canonical systems that show the effects of frustration in both heat capacity and dynamical response. In both instances, microscopic ordering principles on the lattice lead to a macroscopic degeneracy of configurations, i.e. the entropy is not zero at zero temperature. This degeneracy in spin ice may also be modified or lifted by lattice imperfections, external pressure, or magnetic field. Unfortunately, these effects are difficult to model or predict, because existing experimental techniques cannot directly observe the local ordering, near lattice defects or otherwise. To address this long outstanding problem, recent interest has focused on fabricating systems that allow the effects of frustration to be physically modeled and the resulting local configurations to be directly observed.