Tunneling spectra of individual magnetic endofullerene molecules

We report measurements of electron tunneling spectra for individual N@C$_{60}$ molecules, a spin-3/2 endohedral fullerene. The molecules were measured at low temperature in electromigrated break-junctions in the single-electron transistor configuration. We observe that the N@C$_{60}$ devices exhibit a spin-state transition as a function of applied magnetic field which was not observed in C$_{60}$ control devices. The nature of this transition enables us to identify the charge and spin states of the molecule. The spectra of N@C$_{60}$ devices also exhibit low-energy excited states and signatures of non-equilibrium spin excitations predicted for this molecule. The experimental spectra can be reproduced theoretically by accounting for the exchange interaction between the nitrogen spin and electron(s) on the C$_{60}$ cage.