Magnetic Resonance Imaging of Single Organic Radicals with Sub-Molecular Resolution

Interest in the magnetism of organic compounds is growing because of new organic magnets, spin-based electronics and the diverse properties of magnetic edge states in graphene nanoribbons. Electron spin resonance spectroscopy combined with the scanning tunneling microscopy has recently been developed as a powerful tool to address individual magnetic atoms and molecules at the atomic scale. Here we demonstrate electron spin resonance and magnetic resonance imaging of all-organic radical anions adsorbed on a protective thin insulating film grown on a metal support. We show that using the highly localized exchange field of the magnetic tip apex allows visualization of the delocalized spin density with sub-molecular resolution, enabling spin-density tomography that can distinguish similar molecular species. These results provide new opportunities for visualizing spin density and magnetic interactions at the atomic scale.