Transverse Magnetic Anisotropy in Mn12-acetate: Direct Determination by Inelastic Neutron Scattering

TL;DR

This study uses high-resolution inelastic neutron scattering to precisely determine the spin Hamiltonian parameters of Mn12-acetate, revealing non-axial symmetry and supporting a model involving multiple molecular isomers with different magnetic properties.

Contribution

It provides the most accurate spin Hamiltonian parameters for Mn12-acetate and demonstrates the presence of non-axial symmetry, supporting a model of multiple isomers with distinct parameters.

Findings

Non-zero rhombic term improves INS peak agreement.

Deuteration enhances measurement accuracy.

Supports multiple isomer model over symmetry-lowering due to dislocations.

Abstract

A high resolution inelastic neutron scattering (INS) study of fully deuterated Mn$_{12}$-acetate provides the most accurate spin Hamiltonian parameters for this prototype single molecule magnet so far. The Mn$_{12}$-clusters deviate from axial symmetry, a non-zero rhombic term in the model Hamiltonian leading to excellent agreement with observed positions and intensities of the INS peaks. The following parameter set provides the best agreement with the experimental data: $D=-0.0570(1)$ meV, $B_{4}^0=-2.78(7)\cdot 10^{-6}$ meV, $B_{4}^4=-3.2(6)\cdot 10^{-6}$ meV and $\mid$\textit{E}$\mid =6.8(15)\cdot 10^{-4}$ meV. Crystal dislocations are not the likely cause of the symmetry lowering. Rather, this study lends strong support to a recently proposed model, which is based on the presence of several molecular isomers with distinct spin Hamiltonian parameters.