Probing Intermolecular Magnetic Interactions in a Metal Complex by Inelastic Neutron Scattering*

Molecular magnetic materials, such as single-molecule magnets (SMMs) composed of a single paramagnetic metal center complexed by organic ligands, are of intense interest for their potential applications as traditional bits in high-density data storage devices or as qubits in quantum computers. It is generally assumed that these paramagnetic centers behave independently of one another. However, spin-spin couplings among the molecules are known to contribute to magnetic relaxation. Few techniques exist to directly probe the intermolecular magnetic interactions. We have utilized inelastic neutron scattering (INS) to reveal these interactions in a field-induced single-molecule magnet, Mn(TPP)Cl (TPP^2- = meso-tetraphenylporphyrinate) as an oscillatory Q-dependence of the magnetic transition. We analyze the INS results using a combination of Heisenberg spin-spin exchange for intermolecular spin interactions in combination with single-ion excitations.