  Due to the predominantly surface character of graphene, it is highly suitable
for functionalization with external atoms and/or molecules leading to a
plethora of new and interesting phenomena. Here we show ferromagnetic
properties of hydrogen-functionalized epitaxial graphene on SiC. Ferromagnetism
in such a material is not directly evident as it is inherently composed of only
non-magnetic constituents. Our results nevertheless show strong ferromagnetism,
which cannot be explained by simple magnetic impurities. The ferromagnetism is
unique to hydrogenated epitaxial graphene on SiC, where interactions with the
interfacial buffer layer play a crucial role. We argue that the origin of the
observed ferromagnetism is governed by electron correlation effects of the
narrow Si-dangling-bond (Si-DB) states in the buffer layer exchange-coupled to
localized states in the hydrogenated graphene layer. This forms a
quasi-three-dimensional ferromagnet with a Curie temperature higher than 300 K.
