Inelastic neutron scattering study of the molecular grid nanomagnet Mn-[3x3]

The spin Hamiltonian of a supramolecular planar grid formed by nine Mn(II) ions in an almost square geometry has been determined from the analysis of inelastic neutron scattering spectra. The experimental data have been interpreted in the framework of a theoretical model containing all the main interactions present in the system. Difficulties related with the dimension of the Hilbert space have been overcome by exploiting both the irreducible tensor operator technique and the Lanczos algorithm. The energy spectrum consists of level multiplets with an almost definite value of the total spin S. The ground multiplet has S=5/2, and the lowest-lying excited multiplets have (in order of increasing energy) S=7/2, S=3/2, S=3/2, and S=9/2. These multiplets are separated by the isotropic exchange and split by the anisotropic interactions. The two lowest manifolds of the exchange part of the spin Hamiltonian belong to the same irreducible representation of the molecular symmetry group and substantial mixing between them is demonstrated.