Abstract
Measurements of proton nuclear magnetic resonance () spectra and relaxation and of muon spin relaxation () have been performed as a function of temperature and external magnetic field on two isostructural lanthanide complexes, Er(trensal) and Dy(trensal) [where ], featuring crystallographically imposed trigonal symmetry. Both the nuclear and muon λ longitudinal relaxation rates (LRRs) exhibit a peak for temperatures < 30 K, associated to the slowing down of the spin dynamics, and the width of the NMR absorption spectra starts to increase significantly at ∼ 50 K, 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 determined by the spin slowing down at low temperature. Further, for the spectral width does not follow the temperature behavior of the magnetic susceptibility χ. 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 and , dominating for < 30 K and , respectively. Finally, the observed flattening of LRR for < 5 K is suggested to have a quantum origin.
- Received 20 May 2019
- Revised 10 September 2019
DOI:https://doi.org/10.1103/PhysRevB.100.174416
©2019 American Physical Society