  Electrical injection in organic semiconductors is a key prerequisite for the
realization of organic spintronics. Using density-functional theory
calculations we report the effect of electron transfer into the organic
molecule Alq$_3$. Our first-principles simulations show that electron injection
spontaneously spin-polarizes non-magnetic Alq$_3$ with a magnetic moment
linearly increasing with induced charge. An asymmetry of the Al--N bond lengths
leads to an asymmetric distribution of injected charge over the molecule. The
spin-polarization arises from a filling of dominantly the nitrogen $p_z$
orbitals in the molecule's LUMO together with ferromagnetic coupling of the
spins on the quinoline rings.
