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.
@article{arxiv.cond-mat/0203480,
title = {Exchange couplings in the magnetic molecular cluster Mn12Ac},
author = {N. Regnault and Th. Jolicoeur and R. Sessoli and D. Gatteschi and M. Verdaguer},
journal= {arXiv preprint arXiv:cond-mat/0203480},
year = {2009}
}
Comments
15 pages, 6 figures, submitted to Phys Rev B, corrected a misTeX: values of J1, J2 have changed, refs updated