Room-temperature long-range ferromagnetic order in a confined molecular monolayer

In recent years, research on spin ordering phenomena has broadened to include intermolecular exchange interactions in organic–inorganic crystals and goes beyond the traditional focus on interatomic interactions. However, a crystallized framework used for stabilizing parallel spin alignment through an ordered lattice is indispensable to ferromagnetism. Here we demonstrate room-temperature ferromagnetic order in two-dimensional confined molecule-based monolayers. The confinement effect of the van der Waals interlayer space enables cobaltocene molecules to self-assemble into a monolayer with a honeycomb-like configuration. The spontaneous uniform spin orientation—ferromagnetic coupling—is established by an intermolecular vibronic superexchange interaction, involving a cooperative dynamic Jahn–Teller effect in the confined cobaltocene monolayer. The molecular cobaltocene monolayers exhibit a ferromagnetic transition temperature above room temperature and have a large saturation magnetization.