Artificial spin ice consists of arrays of lithographically fabricated single-domain ferromagnetic elements, arranged in different geometries such that the magnetostatic interactions between the moments are frustrated.  Because we can both design the lattice geometries and probe the individual moments, these systems allow us to study the accommodation of frustration with exquisite detail and flexibility.  These systems were first studied in a collaboration at Penn State, supported by a seed grant from the Penn State MRSEC in the early 2000’s.  Since that time, many groups around the world have explored a range of interesting physics from these systems. 

I will report results from a number of recent experimental efforts in artificial spin ice. The first area of research consists of studies of artificial spin ice arrays with lattice geometries that are unavailable in natural systems and are specifically designed to manifest novel forms of frustration. These so-called “vertex frustrated” lattices demonstrate that novel forms of frustration result in unusual collective behavior. The second area of research is detailed electrical transport studies of connected artificial spin ice systems. We find that appropriate micromagnetic modeling allows us to explain the fascinating collective magnetoresistance phenomena in these systems and reveals the crucial role of the vertex regions in how electronic transport is manifested.   I will conclude with a discussion of ordering among non-Ising magnetic elements, and a study of the noise associated with a plasma of monopole-like elementary excitations.

References: Le et al., Physical Review B 95, 060405(R) (2017); Nisoli et al. Nature Physics 13, 200 (2017); Lao et al., Nature Physics 14, 723 (2018); Sklenar et al., Nature Physics 15, 191 (2019); Goryca et al., Phys. Rev. X 11, 011042 (2021); Schiffer and Nisoli, APL 118, 110501 (2021); Zhang et al., Nature Communications 12, 6514 (2021), Saglam et al., Nature Physics in press (2022).