Polarisation-dependent single-pulse ultrafast optical switching of an elementary ferromagnet

TL;DR

This paper demonstrates that a single, circularly polarized ultrafast laser pulse can reversibly switch the magnetisation of bulk nickel within femtoseconds, revealing a new mechanism for optical control of elementary ferromagnets.

Contribution

It introduces a novel ultrafast optical switching method for elementary ferromagnets using circularly polarized light, supported by detailed electronic structure simulations.

Findings

Single laser pulse can reverse nickel magnetisation

Ultrafast light-induced torques are key to switching

Rich intra-atomic orbital dynamics observed

Abstract

The ultimate control of magnetic states of matter at femtosecond (or even faster) timescales defines one of the most pursued paradigm shifts for future information technology. In this context, ultrafast laser pulses developed into extremely valuable stimuli for the all-optical magnetisation reversal in ferrimagnetic and ferromagnetic alloys and multilayers, while this remains elusive in elementary ferromagnets. Here we demonstrate that a single laser pulse with sub-picosecond duration can lead to the reversal of the magnetisation of bulk nickel, in tandem with the expected demagnetisation. As revealed by realistic time-dependent electronic structure simulations, the central mechanism is ultrafast light-induced torques acting on the magnetisation, which are only effective if the laser pulse is circularly polarised on a plane that contains the initial orientation of the magnetisation. We map the laser pulse parameter space enabling the magnetisation switching and unveil rich intra-atomic orbital-dependent magnetisation dynamics featuring transient inter-orbital non-collinear states. Our findings open further perspectives for the efficient implementation of optically-based spintronic devices.