Spin relaxation in Mn12-acetate

TL;DR

This paper derives and calculates the magnetization relaxation in Mn12-acetate crystals, showing good agreement with experimental data and revealing multiple transition pathways and new spin-phonon coupling constants.

Contribution

It provides a comprehensive theoretical model for spin relaxation in Mn12-acetate, including resonance effects and explicit calculation of previously unknown coupling constants.

Findings

Relaxation rate matches experimental data across resonance peaks.

Resonance peaks exhibit Lorentzian shape consistent with observations.

Multiple transition paths significantly contribute to relaxation.

Abstract

We present a comprehensive derivation of the magnetization relaxation in a Mn12-acetate crystal based on thermally assisted spin tunneling induced by quartic anisotropy and weak transverse magnetic fields. The overall relaxation rate as function of the magnetic field is calculated and shown to agree well with data including all resonance peaks. The Lorentzian shape of the resonances is also in good agreement with recent data. A generalized master equation including resonances is derived and solved exactly. It is shown that many transition paths with comparable weight exist that contribute to the relaxation process. Previously unknown spin-phonon coupling constants are calculated explicitly.