Exchange couplings in the magnetic molecular cluster Mn12Ac

TL;DR

This paper models the magnetic interactions in Mn12Ac by determining exchange couplings through exact diagonalization, reproducing experimental magnetization data, and predicting excited state energy levels.

Contribution

It introduces a method to accurately determine exchange couplings in Mn12Ac using a Heisenberg model and Lanczos algorithm, aligning theoretical predictions with experimental observations.

Findings

Exchange couplings reproduce magnetization curve

Predicted excited states at 37K and 67K above ground state

Confirmed S=10 ground state with a 35K gap to S=9 state

Abstract

The magnetic properties of the molecular cluster Mn12Ac are due to the four Mn3+ ions which have spins S=3/2 and the eight Mn4+ ions with spins S=2. These spins are coupled by superexchange mechanism. We determine the four exchange couplings assuming a Heisenberg-type interaction between the ions. We use exact diagonalization of the spin Hamiltonian by a Lanczos algorithm and we adjust the couplings to reproduce the magnetization curve of Mn12Ac. We also impose the constraint of reproducing a gap of 35K between a S=10 ground state and a first excited state with S=9. We predict that there is an excited level with S=8 at 37K above the ground state, only slightly above the S=9 excited state which lies at 35K and the next excited state is a S=9 multiplet at 67K above the S=10 ground state.