What relaxes muon spins in molecular nanomagnets?

TL;DR

This study investigates the mechanisms behind muon spin relaxation in molecular nanomagnets, revealing that electronic spin fluctuations and nuclear field effects govern relaxation, with a transition to static magnetic order at low temperatures.

Contribution

It demonstrates that muon spin relaxation in MNMs is driven by electronic spin dynamics and nuclear field fluctuations, providing new insights into low-temperature magnetic ordering.

Findings

Muon spin relaxation is caused by electronic spin fluctuations.

Dynamic processes freeze out at low temperatures.

A transition to static magnetic order occurs below 2 K.

Abstract

We address the cause of the unusual muon spin relaxation (muSR) results on molecular nanomagnets (MNMs). Through measurements on protonated and deuterated samples of the MNMs Cr7Mn (S=1) and Cr8 (S=0), we show that the muon spin for $S \neq 0$ MNMs is relaxed via dynamic fluctuations of the electronic spins. A freezing out of dynamic processes occurs on cooling and at low temperatures the muon spins are relaxed by the electronic spins which themselves are dephased by incoherent nuclear field fluctuations.We observe a transition to a state of static magnetic order of the MNM electronic spins in Cr7Mn below 2 K.