Lattice effects on the spin dynamics in antiferromagnetic molecular rings

TL;DR

This paper explores how lattice effects influence spin dynamics in antiferromagnetic molecular rings, revealing that symmetry changes can significantly affect nuclear relaxation mechanisms through spin-phonon interactions.

Contribution

It introduces a microscopic model for spin-phonon interactions in AF molecular rings, highlighting the impact of symmetry and anisotropy on spin susceptibility and nuclear relaxation.

Findings

Susceptibility exhibits a Lorentzian profile at low frequencies

All spin operators contribute to dynamics at non-zero wave vectors

Symmetry alterations qualitatively change nuclear relaxation mechanisms

Abstract

We investigate spin dynamics in antiferromagnetic (AF) molecular rings at finite temperature in the presence of spin-phonon (s-p) interaction. We derive a general expression for the spin susceptibility in the weak s-p coupling limit and then we focus on the low-frequency behavior, in order to discuss a possible microscopic mechanism for nuclear relaxation in this class of magnetic materials. To lowest order in a perturbative expansion, we find that the susceptibility takes a Lorentzian profile and all spin operators ($S^x$, $S^y, S^z$) contribute to spin dynamics at wave vectors $q\ne 0$. Spin anisotropies and local s-p coupling play a key role in the proposed mechanism. Our results prove that small changes in the spatial symmetry of the ring induce qualitative changes in the spin dynamics at the nuclear frequency, providing a novel mechanism for nuclear relaxation. Possible experiments are proposed.