Low-Temperature Quantum Relaxation in a System of Magnetic Nanomolecules

TL;DR

This paper explains low-temperature quantum relaxation in magnetic nanomolecules by considering nuclear spins and dipolar interactions, revealing a $\

Contribution

It introduces a model incorporating nuclear spin dynamics and dipolar interactions to explain quantum relaxation phenomena in magnetic nanomolecules.

Findings

Relaxation follows a $\

Short-time relaxation exhibits a $\

Results are applicable to Fe8 systems.

Abstract

We argue that to explain recent resonant tunneling experiments on crystals of Mn$_{12}$ and Fe$_8$, particularly in the low-T limit, one must invoke dynamic nuclear spin and dipolar interactions. We show the low-$T$, short-time relaxation will then have a $\sqrt{t/\tau}$ form, where $\tau $ depends on the nuclear $T_2$, on the tunneling matrix element $\Delta_{10}$ between the two lowest levels, and on the initial distribution of internal fields in the sample, which depends very strongly on sample shape. The results are directly applicable to the $Fe_8$ system. We also give some results for the long-time relaxation.