I. Mirebeau, M. Hennion, H. Casalta, H. Andres, H. U. Güdel, V. Irodova and A. Caneschi
The Mn₁₂-acetate spin cluster
ILL Annual Report 99, 48-49 (2000)                 

Abstract: Mn₁₂-acetate is a ferrimagnetic spin cluster with total spin S = 10, providing the first and most well known example of macroscopic quantum tunneling of magnetisation. By inelastic neutron scattering we separated the energy levels corresponding to the splitting of the ground state. We could measure accurately, and for the first time in zero field, a very small energy term, responsible for the quantum tunneling process.