The transfer and manipulation of angular momentum lie at the heart of spintronics. Recent experiments have revealed that angular momentum can flow between spins and phonons on ultrafast timescales [1], yet the microscopic mechanisms remain underexplored. Here, we investigate spin-phonon coupling in magnetic materials using two fully ab initio approaches. Ehrenfest nuclear dynamics combined with time-dependent density functional theory demonstrates that ultrafast demagnetization in FePt generates optical phonons carrying finite angular momentum [2]. Complementarily, a novel first-principles framework [3] for magnon-phonon interactions uncovers chiral phonons in Fe arising from a chirality-selective magnon-phonon hybridization [4]. These results highlight phonon angular momentum as a dynamic degree of freedom and provide new insights into ultrafast spin-lattice interactions and the emergence of hybrid quasiparticles.
References:
[1] Tauchert et al., Nature 602, 73 (2022); Luo et al., Science 382, 698 (2023).
[2] Mrudul et al., PRB 112, L180407 (2025).
[3] Mankovsky et al., PRL 129, 067202 (2022).
[4] Weißenhofer et al., PRL 135, 216701 (2025).