Nuclear spin driven resonant tunnelling of magnetisation in Mn12 acetate

TL;DR

This paper investigates the role of nuclear spins in quantum tunnelling of magnetisation in Mn12 acetate, providing experimental evidence for their influence at very low temperatures through a novel 'hole digging' method.

Contribution

It introduces a new experimental approach to measure local fluctuating fields and demonstrates the influence of nuclear spins on quantum tunnelling in Mn12 acetate at ultra-low temperatures.

Findings

Nuclear spins significantly affect resonance tunnelling at 0.04-0.3K.

Homogeneous line width broadening observed at 1.5-4K matches theoretical predictions.

Experimental 'hole digging' method effectively measures intrinsic line width broadening.

Abstract

Current theories still fail to give a satisfactory explanation of the observed quantum phenomena in the relaxation of the magnetisation of the molecular cluster Mn12 acetate. In the very low temperature regime, Prokof'ev and Stamp recently proposed that slowly changing dipolar fields and rapidly fluctuating hyperfine fields play a major role in the tunnelling process. By means of a faster relaxing minor species of Mn12ac and a new experimental 'hole digging' method, we measured the intrinsic line width broadening due to local fluctuating fields, and found strong evidence for the influence of nuclear spins on resonance tunnelling at very low temperatures (0.04 - 0.3K). At higher temperature (1.5 - 4K), we observed a homogeneous line width broadening of the resonance transitions being in agreement with a recent calculation of Leuenberger and Loss.