Superferromagnetism and domain-wall topologies in artificial 'pinwheel' spin ice

TL;DR

This study investigates how a simple geometric modification in artificial spin ice induces superferromagnetism and diverse domain-wall topologies, revealing controllable spin reversal dynamics and potential device applications.

Contribution

It demonstrates that a 45-degree rotation in pinwheel artificial spin ice induces superferromagnetism and novel domain-wall configurations, advancing understanding of magnetic ordering in engineered nanostructures.

Findings

Rotation changes magnetic order from antiferromagnetic to ferromagnetic.

Observation of mesoscopic domain growth and various domain-wall types.

Control of spin reversal via external magnetic field orientation.

Abstract

For over ten years, arrays of interacting single-domain nanomagnets, referred to as artificial spin ices, have been engineered with the aim to study frustration in model spin systems. Here, we use Fresnel imaging to study the reversal process in 'pinwheel' artificial spin ice, a modified square ASI structure obtained by rotating each island by some angle about its midpoint. Our results demonstrate that a simple 45{\deg} rotation changes the magnetic ordering from antiferromagnetic to ferromagnetic, creating a superferromagnet which exhibits mesoscopic domain growth mediated by domain wall nucleation and coherent domain propagation. We observe several domain-wall configurations, most of which are direct analogues to those seen in continuous ferromagnetic films. However, novel charged walls also appear due to the geometric constraints of the system. Changing the orientation of the external magnetic field allows control of the nature of the spin reversal with the emergence of either 1-D or 2-D avalanches. This unique property of pinwheel ASI could be employed to tune devices based on magnetotransport phenomena such as Hall circuits.