Multiple Spin-Phonon Relaxation Pathways in a Kramer Single-Ion Magnet

TL;DR

This study uses first-principles calculations and machine learning to analyze spin-phonon relaxation pathways in Co(II) single-ion magnets, revealing how phonons influence low-temperature spin dynamics and guiding future magnet design.

Contribution

It introduces a combined first-principles and machine learning approach to elucidate atomistic spin-phonon relaxation mechanisms in single-ion magnets.

Findings

Low-temperature spin dynamics are dominated by THz phonons.

Both Orbach and Raman relaxation channels involve excited spin states.

Intra-molecular motions significantly influence relaxation mechanisms.

Abstract

We present a first-principles investigation of spin-phonon relaxation in a molecular crystal of Co(II) single-ion magnets. Our study combines electronic structure calculations with machine-learning force fields and unravels the nature of both the Orbach and the Raman relaxation channels in terms of atomistic processes. We find that although both mechanisms are mediated by the excited spin states, the low temperature spin dynamics is dominated by phonons in the THz energy range, which partially suppress the benefit of having a large magnetic anisotropy. This study also determines the importance of intra-molecular motions for both the relaxation mechanisms and paves the way to the rational design of a new generation of single-ion magnets with tailored spin-phonon coupling.