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arXiv · 1905.08216

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

E. Lucaccini·L. Sorace·F. Adelnia·S. Sanna·P. Arosio·M. Mariani·S. Carretta·Z. Salman·F. Borsa·A. Lascialfari
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Abstract

Measurements of proton Nuclear Magnetic Resonance (1H NMR) 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) featuring crystallographically imposed trigonal symmetry. Both the nuclear 1/T1 and muon $λ$ 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 $τ$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 $τ$LT and $τ$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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E. Lucaccini, L. Sorace, F. Adelnia, S. Sanna, P. Arosio, M. Mariani, S. Carretta, Z. Salman, F. Borsa, A. Lascialfari. 2019-10-25. NMR and $μ^{+}$SR detection of unconventional spin dynamics in Er(trensal) and Dy(trensal) molecular magnets. https://doi.org/10.1103/physrevb.100.174416

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