All-optical magnetization reversal via x-ray magnetic circular dichroism

TL;DR

This paper demonstrates that femtosecond circularly polarized x-ray pulses can deterministically reverse magnetization in a ferromagnetic multilayer, leveraging x-ray magnetic circular dichroism and resonant excitation at the Pt L3 edge.

Contribution

It introduces the novel use of x-ray photon helicity to control magnetic order parameters, enabling all-optical magnetization switching with element-specific and ultrafast capabilities.

Findings

Magnetization reversal depends on x-ray pulse helicity.

Switching is resonant at the Pt L3 edge.

Helicity-dependent excitation involves core-level to valence state transitions.

Abstract

Light polarization is one of the most fundamental features, equivalent to energy and coherence. Magnetism changes light polarization, and vice versa. The irradiation of intense circularly polarized femtosecond pules to magnetic materials can alter the magnetic orders and elementary excitations, particularly in the visible to infrared spectral regions. Furthermore, the recent development of x-ray free-electron laser enables the element-specific trace of the ultrafast dynamics with high time and spatial resolution. However, the light helicity of x-ray photons has not yet been used to control order parameters in condensed matter materials, not limited to such magnetic phenomenon. Here, we demonstrate the deterministic magnetization reversal of a ferromagnetic Pt/Co/Pt multilayer solely by irradiating femtosecond pulses of circularly polarized hard x-rays. The observed all-optical magnetization switching depends on the helicity of incident x-ray pulses and is strongly resonant with the photon energy at the Pt $L_3$ edge. These results originate in the x-ray magnetic circular dichroism of Pt, involving helicity-dependent excitation from the 2$p_{3/2}$ core level to the exchange-split 5$d$ valence states owing to the magnetic proximity effect with Co. These findings mark a new frontier for examining interactions between light and matter in the x-ray region.