Submillimeter spectroscopy of -Ac magnetic clustersA. A. Mukhin, V. D. Travkin, A. K. Zvezdin, S. P. Lebedev, A. Caneschi and D. GatteschiEurophys. Lett., 44 6 (1998) 778-782DOI: https://doi.org/10.1209/epl/i1998-00541-0