Entanglement in supramolecular spin systems of two weakly coupled antiferromagnetic rings (purple Cr7Ni)

We characterize supramolecular magnetic structures, consisting of two weakly coupled antiferromagneticrings, by low-temperature specific heat, susceptibility, magnetization and electron paramagneticresonance measurements. Intra- and inter-ring interactions are modeled through a microscopic spin-Hamiltonian approach that reproduces all the experimental data quantitatively and legitimates the use ofan effective two-qubit picture. Spin entanglement between the rings is experimentally demonstratedthrough magnetic susceptibility below 50 mK and theoretically quantified by the concurrence.