Atomic-scale control of spin transport in exchange-coupled molecules
Spin transport between coupled spins is governed by tunneling and exchange interactions, yet their microscopic relation in real space has remained experimentally elusive. To address this, we functionalize the tip of a scanning tunneling microscope with a single molecule and use it as a movable spin sensor positioned above a second molecule on a ferromagnetic surface, forming an exchange-coupled molecular junction. From the same spectroscopic dataset, we independently extract the junction conductance, exchange coupling, and spin polarization with atomic-scale resolution. Conductance and exchange display nearly identical spatial dependences, consistent with a minimal Hubbard description in which both are governed by the same hopping matrix between the molecular frontier orbitals. In contrast, the spin polarization depends on the orbital composition and the relative weight of the resulting transport channels. These results establish a real-space connection between tunneling, exchange, and spin transport in magnetically coupled molecules.