We combine spin-polarized scanning tunneling microscopy with quantum master equation analysis to investigate the spin dynamics of the single atom magnet Dy on graphene/Ir(111). By performing reading and writing experiments, we show that the strongly spin polarized $5d6s$ valence shells, as well as their intra-atomic exchange coupling to the $4f$ shell, determine the pathways for magnetization relaxation and thus the spin dynamics. The good quantum number that determines which states are stable and which mechanisms for reversal exist in a given crystal field is the atomic total angular momentum $J_z^{\mathrm{tot}}$ and not the commonly considered $J_z^{4f}$ of the $4f$ shell only.

• Received 19 October 2022
• Revised 17 January 2023
• Accepted 10 February 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.106702

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society