55Mn nuclear spin relaxation in the truly axial single-molecule magnet Mn12-t-butylacetate thermally-activated down to 400 mK

We report on the measurements of the spin–lattice relaxation time, T₁, of Mn₁₂O₁₂(O₂CCH₂Bu^t)₁₆(CH₃OH)₄ · CH₃OH, a truly axial symmetry Mn₁₂ single-molecule magnet (SMM), with the view to examining the role of point symmetry and lattice-solvate molecules in this Mn₁₂ SMM. The measurements were made over 0.390–1.8 K, on freshly prepared single crystals which afforded much higher spectral resolution than magnetically aligned powder. The measured T₁ is found to be thermally activated, and follows either a T² or exponential behavior over 0.390–0.7 K, in contrast to the temperature-independent behavior for Mn₁₂-acetate, where Jahn–Teller isomers are thought to be the origin of the temperature-independent nuclear relaxation mechanism.