Comment on 'Pulsed field studies of the magnetization reversal in molecular nanomagnets'

TL;DR

This paper critiques a recent study on magnetization reversal in Mn12-ac nanomagnets, proposing an alternative explanation involving thermal avalanches triggered by defect molecules, and suggests a method to test this hypothesis.

Contribution

It introduces an alternative thermal avalanche explanation for magnetization steps, challenging the previous collective dipolar relaxation interpretation.

Findings

Thermal avalanches can explain magnetization steps.

Defect molecules act as triggers for avalanches.

Proposed test method to distinguish mechanisms.

Abstract

In a recent paper, cond-mat/0404041, J. Vanacken et al. reported experimental studies of crystals of Mn12-ac molecular nanomagnets in pulsed magnetic fields with sweep rates up to 4000 T/s. Steps in the magnetization curve were observed. The data were explained by collective dipolar relaxation. We give here an alternative explanation that is based on thermal avalanches triggered by defect molecules (faster relaxing species). These species are always present in Mn12-ac molecular nanomagnets. We propose a simple method to test this interpretation. Note that we do not question the possibility of collective effects that are bassed on spin--spin interactions.