4D visualization of the photoexcited coherent magnon by an X-ray free electron laser

TL;DR

This paper demonstrates the use of X-ray free electron lasers to visualize and analyze the dynamics of photoexcited coherent magnons in a multiferroic material, advancing ultrafast magnetic imaging techniques.

Contribution

It introduces a novel method using resonant magnetic X-ray diffraction with XFELs to observe coherent magnons in space and time, providing new insights into ultrafast spin dynamics.

Findings

Visualized photoexcited coherent magnons in a multiferroic material.

Observed large amplitude, long-lived magnetic oscillations.

Revealed significant magnetic-field changes induced by magnons.

Abstract

X-ray free electron lasers (XFEL) create femtosecond X-ray pulses with high brightness and high longitudinal coherence allowing to extend X-ray spectroscopy and scattering techniques into the ultrafast time-domain. These X-rays are a powerful probe for studying coherent quasiparticle excitations in condensed matter triggered by an impulsive optical laser pump. However, unlike coherent phonons, other quasiparticles have been rarely observed due to small signal changes and lack of standards for the identification. Here, we exploit resonant magnetic X-ray diffraction using an XFEL to visualize a photoexcited coherent magnon in space and time. Large intensity oscillations in antiferromagnetic and ferromagnetic Bragg reflections from precessing moment are observed in a multiferroic Y-type hexaferrite. The precession trajectory reveals that a large, long-lived, photoinduced magnetic-field changes the net magnetization substantially through the large-amplitude of the magnon. This work demonstrates an efficient XFEL probe for the coherent magnon in the spotlight for opto-spintronics application.