The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

We present an x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon pi-states, hydrogen-mediated electronic states also exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top approximate to 10 nm of the irradiated sample where the average magnetization reaches similar or equal to 15 emu g(-1) at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin to that found in proton-bombarded graphite. Our findings also show that the magnetic properties of graphite surfaces, thin films or two-dimensional graphene samples can be reliably studied using soft x-ray dichroism. Fundamental new insights into the magnetic properties of carbon-based systems can thus be obtained.