Exchange constants and spin dynamics in Mn12-acetate

TL;DR

This study uses inelastic neutron scattering and a Heisenberg model to analyze the magnetic exchange interactions and spin dynamics in Mn12-acetate, revealing dominant exchange constants and matching experimental excitations.

Contribution

It provides a detailed microscopic model of Mn12-acetate's magnetic interactions, combining INS data with susceptibility fitting and numerical diagonalization for the first time.

Findings

Two dominant exchange constants around 65 K (~5.5 meV) identified.

Qualitative agreement between model predictions and INS data.

Insights into the low-lying spin excitations of Mn12-acetate.

Abstract

We have obtained new inelastic neutron scattering (INS) data for the molecular magnet Mn12-acetate which exhibit at least six magnetic peaks in the energy range 5-35 meV. These are compared with a microscopic Heisenberg model for the 12 quantum spins localised on the Mn ions, coupled by four inequivalent magnetic exchange constants. A fit to the magnetic susceptibility under the constraint that the spin of the ground state be S=10 yields two dominant exchange constants of very similar value, J1 ~ J2 ~ 65 K (~ 5.5 meV), and two smaller exchange constants J3 and J4. We compute the low-lying excitations by exact numerical diagonalisation and demonstrate that the parameters determined from the ground state and susceptibility fit provide qualitative agreement with the excitations observed by INS.