Artificial spin ice: Progress and future directions of the field

Geometrical magnetic frustration arises from the geometry of a well-ordered structure in which interactions between pairs of magnetic moments cannot all be satisfied. This phenomenon occurs naturally in pyrochlore spin ice materials that share the same geometrical frustration as hydrogen ion positions in frozen water. However, individual atomic spins within a material are difficult to probe experimentally and difficult to arrange in precisely controllable geometries.

In 2006, the concept of artificial spin ice was first introduced in a study coauthored by Peter Schiffer and Cristiano Nisoli, where they created lithographically fabricated arrays of single-domain ferromagnetic islands designed to mimic the frustration of the spin ice materials. Schiffer and Nisoli review progress in the field of artificial spin ice since their 2006 study, as well as future directions and applications.

The intrinsic geometrical flexibility of lithography has allowed researchers to transcend the simple structures of early artificial spin ice studies. The field includes novel bespoke periodic and aperiodic geometries not seen in nature.

After fabrication, the individual moment orientations and collective behavior of the extended systems can be examined with imaging techniques, such as magnetic force microscopy and photoemission electron microscopy, as well as through electrical transport and ferromagnetic resonance. Such experiments allow the investigation of physical phenomena not easily accessible in, or even entirely absent from, natural magnets.

The field continues to evolve with researchers studying effective magnetic monopole excitations, expanding to fully 3D structures, and exploring unusual ferromagnetism in the material of the nanomagnets. In addition, artificial spin ice structures provide opportunities for technological applications, such as magnonic devices and realizations of novel computing modalities.

Source: “Artificial spin ice: Paths forward,” by Peter Schiffer and Cristiano Nisoli, Applied Physics Letters (2021). The article can be accessed at http://doi.org/10.1063/5.0044790 .