Magnetic field driven dynamics in twisted bilayer artificial spin ice at superlattice angles*

Geometrical designs of interacting nanomagnets have been studied extensively in

the form of two-dimensional arrays called artificial spin ice. These systems are usually

designed to create geometrical frustration and are of interest for the unusual and

often surprising phenomena that can emerge. Advanced lithographic and element

growth techniques have enabled the realization of complex designs that can involve

elements arranged in three dimensions. Using numerical simulations employing the

dumbbell approximation, we examine possible magnetic behaviours for bilayer artificial

spin ice (BASI) in which the individual layers are rotated with respect to

one another. The goal is to understand how magnetization dynamics are affected

by long-range dipolar coupling that can be modified by varying the layer separation

and layer alignment through rotation. We consider bilayers where the layers are

both either square or pinwheel arrangements of islands. Magnetic reversal processes

are studied and discussed in terms of domain and domain wall configurations of the

magnetic islands. Unusual magnetic ordering is predicted for special angles which

define lateral spin superlattices for the bilayer systems.