# NMR and $\mu^{+}$SR detection of unconventional spin dynamics in Er(trensal) and Dy(trensal) molecular magnets

## TL;DR

This study uses NMR and muon spin relaxation to investigate unconventional spin dynamics in Er(trensal) and Dy(trensal) molecular magnets, revealing complex relaxation processes and potential quantum effects at low temperatures.

## Contribution

It provides new insights into the temperature and field dependence of spin relaxation in lanthanide molecular magnets, highlighting the presence of multiple relaxation processes and deviations from standard models.

## Key findings

- Peak in relaxation rates below 30K indicating spin slowing down
- Spectral width increases around 50K, higher than relaxation peaks
- Evidence of multiple relaxation processes with different correlation times

## Abstract

Measurements of proton Nuclear Magnetic Resonance (1H NMR) spectra and relaxation and of Muon Spin Relaxation ($\mu^{+}$SR) have been performed as a function of temperature and external magnetic field on two isostructural lanthanide complexes, Er(trensal) and Dy(trensal) featuring crystallographically imposed trigonal symmetry. Both the nuclear 1/T1 and muon $\lambda$ longitudinal relaxation rates, LRR, exhibit a peak for temperatures T lower than 30K, associated to the slowing down of the spin dynamics, and the width of the NMR absorption spectra starts to increase significantly at T ca. 50K, a temperature sizably higher than the one of the LRR peaks. The LRR peaks have a field and temperature dependence different from those previously reported for all Molecular Nanomagnets. They do not follow the Bloembergen-Purcell-Pound scaling of the amplitude and position in temperature and field and thus cannot be explained in terms of a single dominating correlation time $\tau$c determined by the spin slowing down at low temperature. Further, for T lower than 50K the spectral width does not follow the temperature behavior of the magnetic susceptibility chi. We suggest, using simple qualitative considerations, that the observed behavior is due to a combination of two different relaxation processes characterized by the correlation times $\tau$LT and $\tau$HT, dominating for T lower than 30K and T higher than 50K, respectively. Finally, the observed flattening of LRR for T lower than 5K is suggested to have a quantum origin.

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Source: https://tomesphere.com/paper/1905.08216