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

Measurements of proton nuclear magnetic resonance (H1NMR) spectra and relaxation and of muon spin relaxation (μ+SR) have been performed as a function of temperature and external magnetic field on two isostructural lanthanide complexes, Er(trensal) and Dy(trensal) [where H3trensal=2,2′,2′′-tris-(salicylideneimino)triethylamine], featuring crystallographically imposed trigonal symmetry. Both the nuclear 1/T1 and muon λ longitudinal relaxation rates (LRRs) exhibit a peak for temperatures T < 30 K, associated to the slowing down of the spin dynamics, and the width of the NMR absorption spectra starts to increase significantly at T ∼50 K, a temperature sizably higher than the one of the LRR p…