pi-electron ferromagnetism in metal-free carbon probed by soft x-ray dichroism.

Elemental carbon represents a fundamental building block of matter and the possibility of ferromagnetic order in carbon has attracted widespread attention. However, the origin of magnetic order in such a light element is only poorly understood and has puzzled researchers. We present a spectromicroscopy study at room temperature of proton irradiated metal-free carbon using the elemental and chemical specificity of x-ray magnetic circular dichroism. We demonstrate that the magnetic order in the investigated system originates only from the carbon pi-electron system.