The symmetry of single-molecule magnets dictates their spin quantum dynamics,influencing how such systems relax via quantum tunneling of magnetization(QTM). By reducing a system's symmetry, through the application of a magneticfield or uniaxial pressure, these dynamics can be modified. We reportmeasurements of the magnetization dynamics of a crystalline sample of thehigh-symmetry [Mn12O12(O2CMe)16(MeOH)4]MeOH single-molecule magnet as afunction of uniaxial pressure applied either parallel or perpendicular to thesample's "easy" magnetization axis. At temperatures between 1.8 and 3.3 K,magnetic hysteresis loops exhibit the characteristic steplike features thatsignal the occurrence of QTM. After applying uniaxial pressure to the sample insitu, both the magnitude and field position of the QTM steps changed. The stepmagnitudes were observed to grow as a function of pressure in both arrangementsof pressure, while pressure applied along (perpendicular to) the sample's easyaxis caused the resonant-tunneling fields to increase (decrease). Theseobservations were compared with simulations in which the system's Hamiltonianparameters were changed. From these comparisons, we determined that parallelpressure induces changes to the second-order axial anisotropy parameter as wellas either the fourth-order axial or fourth-order transverse parameter, or toboth. In addition, we find that pressure applied perpendicular to the easy axisinduces a rhombic anisotropy E ~ D/2000 per kbar that can be understood asderiving from a symmetry-breaking distortion of the molecule.
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