Photo-induced switching of magnetisation in the epsilon-near-zero regime

TL;DR

This study demonstrates that mid-infrared pulses at epsilon-near-zero points can effectively switch magnetisation in a magnetic dielectric, highlighting a thermal mechanism for laser-driven magnetic control.

Contribution

It reveals that epsilon-near-zero conditions enable efficient magnetisation switching via thermal effects, challenging the idea that maximum absorption is necessary.

Findings

Labyrinthine domains transform into parallel stripes under mid-infrared excitation.

Magnetisation switching is strongest at epsilon-near-zero points, not at maximum absorption.

Thermal quenching of anisotropy is the primary mechanism for switching.

Abstract

The possibility of controlling spins using ultrashort light and strain pulses has triggered intense discussions about the mechanisms responsible for magnetic re-ordering. All-optical magnetisation switching can be achieved through ultrafast heat-driven demagnetisation or transient modifications of magnetic anisotropy. During the phononic switching of magnetic dielectrics, however, mid-infrared optical excitations can modify the crystal environment via both the thermal quenching of anisotropy and the generation of strain respectively, with the relative distinction between these thermal and non-thermal processes remaining an open question. Here, we examine the effect of mid-infrared pulses tuned to the frequency of optical phonon resonances on the labyrinthine domain structure of a cobalt-doped yttrium iron garnet film. We find that the labyrinthine domains are transformed into stable parallel stripes, and quantitative micromagnetic calculations demonstrate this stems predominantly from a partial quenching of the anisotropy. Contrary to conventional wisdom, however, we find that this heat-facilitated process of magnetisation switching is spectrally strongest not at the maximum of absorbed optical energy but rather at the epsilon-near-zero points. Our results reveal that the epsilon-near-zero condition provides an alternative pathway for laser-driven control of magnetisation, even when the underlying mechanism is primarily thermal.