  The creation of magnetism on non-magnetic semiconductor surfaces is of
importance for the realization of spintronics devices. Especially, the coupling
of electron spins within quantum nanostructures can be utilized for
nanomagnetism applications. Here, we demonstrate, based on first-principles
density-functional theory calculations, that the adsorption of H atoms on the
Si(111)-(7$\times$7) surface induces the spin polarization of surrounding Si
dangling bonds (DBs) and their spin orderings. It is revealed that the H
adsorption on a rest-atom site exhibits a Jahn-Teller-like distortion that
accompanies a charge transfer from the rest atom to the nearest neighboring
adatoms. This charge transfer increases the local density of states of such
three adatoms at the Fermi level, thereby inducing a Stoner-type instability to
produce a ferrimagnetic order of adatom DBs around the adsorbed H atom.
Meanwhile, the H adsorption on an adatom site cannot induce spin polarization,
but, as adsorbed H atoms increase, the ferrimagnetic order of rest-atom DBs
emerges through the charge transfer from rest atoms to adatoms. Our findings
provide a microscopic mechanism of the H-induced spin orderings of Si DBs at
the atomic scale, which paves a novel way to the design of nanoscale magnetism
in the representative semiconductor surface.
