Effects of uniaxial pressure on the quantum tunneling of magnetization in a high-symmetry Mn12 single-molecule magnet

TL;DR

This study investigates how uniaxial pressure affects quantum tunneling of magnetization in a high-symmetry Mn12 single-molecule magnet, revealing pressure-induced modifications to magnetic anisotropy and tunneling behavior.

Contribution

It provides the first detailed experimental analysis of uniaxial pressure effects on QTM in a high-symmetry single-molecule magnet, linking pressure to anisotropy parameter changes.

Findings

Pressure alters the magnitude and position of QTM steps.

Parallel pressure affects second- and fourth-order anisotropy parameters.

Perpendicular pressure induces a measurable rhombic anisotropy.

Abstract

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 magnetic field or uniaxial pressure, these dynamics can be modified. We report measurements of the magnetization dynamics of a crystalline sample of the high-symmetry [Mn12O12(O2CMe)16(MeOH)4]MeOH single-molecule magnet as a function of uniaxial pressure applied either parallel or perpendicular to the sample's "easy" magnetization axis. At temperatures between 1.8 and 3.3 K, magnetic hysteresis loops exhibit the characteristic steplike features that signal the occurrence of QTM. After applying uniaxial pressure to the sample in situ, both the magnitude and field position of the QTM steps changed. The step magnitudes were observed to grow as a function of pressure in both arrangements of pressure, while pressure applied along (perpendicular to) the sample's easy axis caused the resonant-tunneling fields to increase (decrease). These observations were compared with simulations in which the system's Hamiltonian parameters were changed. From these comparisons, we determined that parallel pressure induces changes to the second-order axial anisotropy parameter as well as either the fourth-order axial or fourth-order transverse parameter, or to both. In addition, we find that pressure applied perpendicular to the easy axis induces a rhombic anisotropy E ~ D/2000 per kbar that can be understood as deriving from a symmetry-breaking distortion of the molecule.