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 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 τc determined by the spin slowing down at low temperature. Further, for T<50K 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 τLT and τHT, dominating for T < 30 K and T>50K, respectively. Finally, the observed flattening of LRR for T < 5 K is suggested to have a quantum origin.

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

Mariani M.
Membro del Collaboration Group
;
Lascialfari A.
2019-01-01

Abstract

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 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 τc determined by the spin slowing down at low temperature. Further, for T<50K 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 τLT and τHT, dominating for T < 30 K and T>50K, respectively. Finally, the observed flattening of LRR for T < 5 K is suggested to have a quantum origin.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/1430594
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