Fabrication of Hybrid Artificial Spin Ice Arrays with Periodic Site-Specific Local Magnetic Fields

We describe the microfabrication and magnetic behavior of a composite/hybrid, two-dimensional, magnetostatically interacting array of nanomagnets of Fe and exchange-biased bilayer Fe/IrMn heterostructures. Such an interacting array of nanomagnets, forming an artificial spin ice lattice but with a hybrid structure, has not been demonstrated before. These devices are fabricated of epitaxially grown Fe/IrMn thin films by a two-stage electron beam lithography process involving metal mask transfer and controlled ion milling. Following the epitaxial deposition of Fe/IrMn bilayer films, the first step involves electron beam lithography fabrication of nanomagnet arrays, followed by selective removal of exchange-bias by etching away IrMn layer at specific nanomagnet elements by ion milling. The technique described provides a way to apply a site-specific magnetic field at the nanometer length scale, utilizing the phenomenon of exchange-bias, as demonstrated here for an array with local fields applied at twice the period of the artificial spin ice lattice. This technology can also be readily extended to different spintronic devices requiring spatial distribution of exchange-bias fields.