Pyrochlore Artificial Spin Ice: Advances in Fabrication and Characterization of a 3D Magnetic Metamaterial

Artificial spin ices are magnetic metamaterials consisting of arrays of magnetically coupled nanoscale magnets arranged in various geometries. They display a variety of fascinating phenomena including emergent magnetic monopoles, phase transitions and frustration. 

While the nanomagnets are often arranged in planar arrays, the development of artificial spin ices in three dimensions would allow the exploration of new fundamental phenomena. 3D artificial spin ices are also of interest for neuromorphic computing because of the rich magnetic state space, enhanced connectivity, and increased areal density. Here, a 3D artif cial spin ice based on the pyrochlore lattice found in a spin ice crystal is presented. 

In this Pyrochlore artificial spin ice, disconnected nanomagnets, inclined at an angle to the substrate, are located at four different heights. The nanomagnets are held up by a polymer scaffold fabricated using a combination of two‐photon lithography and pyrolysis. The scaffold consists of sloped nanomagnet supports on tailored hemispherical decoupling structures that ensure uniform shrinkage during pyrolysis. Imaging with magnetic force microscopy indicates that the nanomagnets adopt a variety of magnetic states including single‐domain, s‐, and vortex states, while the necessity for further advances in synchrotron X‐ray imaging techniques tailored to these 3D magnetic architectures is highlighted.