Symmetry of Magnetic Quantum Tunneling in Single Molecule Magnet Mn12-acetate

TL;DR

This study investigates how local molecular environments and disorder influence the symmetry and quantum tunneling behavior in the single molecule magnet Mn12-acetate, revealing the role of local twofold symmetry and Berry phase effects.

Contribution

It demonstrates that local twofold symmetries due to disorder are crucial for magnetic quantum tunneling and provides evidence for Berry phase effects in these molecules.

Findings

Average fourfold symmetry arises from twofold local environments.

Disorder lowers molecular symmetry, affecting tunneling.

Evidence of Berry phase effect consistent with local twofold symmetry.

Abstract

The symmetry of magnetic quantum tunneling has been studied in the prototype single molecule magnet Mn$_{12}$-acetate using a micro-Hall effect magnetometer and superconducting high field vector magnet system. An average crystal fourfold symmetry is shown to be due to local molecular environments of twofold symmetry that are rotated by 90$^o$ with respect to one another, confirming that disorder which lowers the molecule symmetry is at important to magnetic quantum tunneling. We have studied a subset of these lower (twofold) site symmetry molecules and present evidence for a Berry phase effect consistent with a local twofold symmetry.