We consider the effect of adding electrons to a single molecule on its magnetic properties and the resulting transport fingerprints. We analyze a generic model for a metal-organic complex consisting of orbitals with different Coulomb repulsions. We find that by modulating the charge of the molecule by a single electron the total spin can be switched from zero to the maximal value supported by the added electrons, S=3/2. The Nagaoka mechanism is responsible for this charge-sensitivity of the molecular spin. It is shown that fingerprints of these maximal spin states, either as groundstates or low-lying excitations, can be experimentally observed in current-spectroscopy. as either spin blockade at low bias voltage or negative differential conductance and complete current suppression at finite bias.
@article{arxiv.cond-mat/0502091,
title = {Spin blockade in a charge-switchable molecular magnet},
author = {C. Romeike and M. R. Wegewijs and H. Schoeller},
journal= {arXiv preprint arXiv:cond-mat/0502091},
year = {2007}
}