Time-resolved measurement of spin excitations in Cu$_2$OSeO$_3$

TL;DR

This study employs time-resolved x-ray diffraction and ferromagnetic resonance to investigate the dynamic spin configurations in Cu$_2$OSeO$_3$, revealing phase-dependent amplitude and phase responses in different magnetic phases.

Contribution

It demonstrates the use of magnetic diffraction combined with x-ray detected ferromagnetic resonance for time-resolved measurement of spin dynamics in chiral magnets.

Findings

Continuous 180° phase advance in conical mode

180° phase lag in field-polarized mode

Inversion of spin dynamics along the conical axis with field direction

Abstract

Magnetic diffraction in combination with x-ray detected ferromagnetic resonance (DFMR) is a powerful technique for performing time-resolved measurements on individual spin textures. Here, we study the ferromagnetic resonance (FMR) modes of both the conical and field-polarized phases in the chiral magnet Cu$_2$OSeO$_3$. Following the identification of the FMR modes at different temperatures using broadband vector network analyzer FMR, we use DFMR on the crystalline (001) Bragg peak to reveal the time-dependent spin configurations of the selected FMR modes. By being able to measure both the amplitude and phase response of the spin system across the resonance, a continuous phase advance (of 180$^\circ$) in the conical mode, and a phase lag (of 180$^\circ$) in the field-polarized mode is found. By performing dynamic measurements in the conical phase as a function of the linear polarization angle of the x-rays, i.e., successively probing the dynamics of the moments, we find an inversion of the dynamics along the conical axis upon inverting the applied field direction. By allowing for time-resolved measurements of the phase and amplitude of individual magnetic phases, DFMR opens up new opportunities for obtaining a deeper understanding of the complex dynamics of chiral magnets.