Ferromagnetism in molecular decamethylferrocenium tetracyanoethenide (DMeFc TCNE)

Abstract
The temperature and magnetic field dependence of the magnetization and susceptibility of single-crystal decamethylferrocenium tetracyanoethenide (DMeFc TCNE) demonstrate that this material is the first molecular compound with a ferromagnetic ground state. A spontaneous magnetization is observed for T K. The results are consistent with a crossover from a dominance of one-dimensional ferromagnetic exchange interaction to a 3D mean-field-like interaction at ∼16 K. The critical exponents are in accord with mean-field behavior. A generalized Hubbard model is proposed to account for the unusual ferromagnetic exchange interactions in this system.