Low power continuous-wave all-optical magnetic switching in ferromagnetic nanoarrays

TL;DR

This paper demonstrates low-power, deterministic all-optical magnetic switching in ferromagnetic nanoarrays using a focused continuous-wave laser, enabling ultrafast and high-resolution control without complex materials or ultrashort pulses.

Contribution

It introduces a novel low-power, continuous-wave laser method for all-optical magnetic switching in simple ferromagnetic nanomagnets, expanding potential applications.

Findings

Switching achieved with sub-diffraction limit nanomagnets using low-power CW laser.

Deterministic switching depends on asymmetric absorption distribution.

Switching observed in NiFe alloys, not in Co, indicating material dependence.

Abstract

All-optical magnetic switching promises ultrafast, high-resolution magnetisation control with the technological attraction of requiring no magnetic field. Existing all-optical switching schemes are driven by ultrafast transient effects, typically requiring power-hungry femtosecond-pulsed lasers and complex magnetic materials. Here, we demonstrate deterministic, all-optical magnetic switching in simple ferromagnetic nanomagnets (Ni$_{81}$Fe$_{19}$, Ni$_{50}$Fe$_{50}$) with sub-diffraction limit dimensions using a focused low-power, linearly-polarised continuous-wave laser. Isolated nanomagnets are switched across a range of dimensions, laser wavelengths and powers. All square-geometry artificial spin ice vertex configurations are written, including ground-state and energetically-unfavourable `monopole-like' states at powers as low as 2.74 mW. Usually, magnetic switching with linearly polarised light is symmetry-forbidden; however, here the laser spot has a similar size to the nanomagnets, producing an absorption distribution dependent on the relative nanoisland-spot displacement. We attribute the observed deterministic switching to the transient dynamics of this asymmetric absorption. No switching is observed in Co samples, suggesting the multi-species nature of NiFe alloys plays a role in reversal. The results presented here usher in cheap, low-power optically-controlled devices with impact across data storage, neuromorphic computation and reconfigurable magnonics.