  First-principles calculations of the effect of carbon coverage on the atomic,
electronic and magnetic structure of nickel and iron substrates demonstrate
insignificant changes in the interatomic distances and magnetic moments on the
atoms of the metallic substrates. The coverage of the iron surface by mono- and
few-layer graphene induces significant changes in the orbital occupancies and
exchange interactions between the layers in contrast to the case of a nickel
substrate for which changes in the orbital ordering and exchange interactions
are much smaller. Experimental measurements demonstrate the presence of
ferromagnetic fcc-iron in Fe@C nanoparticles and the superparamagnetic behavior
of Ni@C nanoparticles.
