Properties of low-lying excited manifolds in the Mn12 acetate

TL;DR

This study investigates the low-lying excited spin states in Mn12 acetate, revealing multiple S=9 manifolds near the ground state and showing their magnetic anisotropy barriers are comparable to the ground state, enhancing understanding of its magnetic properties.

Contribution

The paper provides a detailed calculation of exchange interactions and energy gaps for low-lying excited states in Mn12 acetate using DFT, clarifying their magnetic anisotropy characteristics.

Findings

Energy gap between ground and first excited state is about 40.5 K.

Several S=9 excited-state manifolds exist above the S=10 ground state.

Anisotropy barriers for excited states are similar to the ground state.

Abstract

Most experimental data on the single-molecule magnet Mn$_{12}$ acetate have been successfully explained by the assumption that the Mn$_{12}$ acetate has an effective ground-state spin of S=10. However, the effect of the low-lying excited manifolds caused by interactions between Mn spins has not been well understood. To investigate the features of the low-lying excited manifolds, the intramolecular exchange interactions are calculated using density-functional theory (DFT). With the calculated exchange parameters, the energy gap between the S=10 ground-state and the first excited-state manifold is calculated by diagonalization of the Heisenberg Hamiltonian. The upper limit on the energy gap is about 40.5 K which is likely to be overestimated due to incomplete treatment of the Coulomb potential within DFT. It is found that there are several S=9 low-energy excited-state manifolds above the S=10 ground-state manifold. The magnetic anisotropy barriers for the low-lying spin excitations are calculated using DFT. Based on the calculations, it is found that the anisotropy barriers for the low-lying excited manifolds are approximately the same as that for the ground-state manifold, which is applicable to other single-molecule magnets such as Mn$_4$.