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

Abstract

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 π-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 ≈10 nm of the irradiated sample where the average magnetization reaches ≃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.