Resonant Tunneling in Truly Axial Symmetry Mn 12 Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling

摘要: Magnetization measurements of a truly axial symmetry ${\mathrm{Mn}}_{12}\mathrm{\text{\ensuremath{-}}}t\mathrm{BuAc}$ molecular nanomagnet with spin ground state $S=10$ show resonant tunneling. This compound has the same magnetic anisotropy as ${\mathrm{Mn}}_{12}\mathrm{\text{\ensuremath{-}}}\mathrm{Ac}$ but molecules are better isolated and crystals have less disorder higher symmetry. Hysteresis loop at several temperatures reveal well-resolved step fine structure which is due to level crossings excited states. All positions can be modeled by simple Hamiltonian. The results establish sharp crossover between thermally assisted pure quantum tunneling, had been previously predicted.