  The understanding of orbital hybridization and spin-polarization at the
organic-ferromagnetic interface is essential in the search for efficient hybrid
spintronic devices. Here, using first-principles calculations, we report a
systematic study of spin-split hybrid states of C$_{60}$ deposited on various
ferromagnetic surfaces: bcc-Cr(001), bcc-Fe(001), bcc-Co(001), fcc-Co(001) and
hcp-Co(0001). We show that the adsorption geometry of the molecule with respect
to the surface crystallographic orientation of the magnetic substrate as well
as the strength of the interaction play an intricate role in the
spin-polarization of the hybrid orbitals. We find that a large
spin-polarization in vacuum above the buckyball can only be achieved if the
molecule is adsorbed upon a bcc-(001) surface by its pentagonal ring. Therefore
bcc-Cr(001), bcc-Fe(001) and bcc-Co(001) are the optimal candidates.
Spin-polarized scanning tunneling spectroscopy measurements on single C$_{60}$
adsorbed on Cr(001) and Co/Pt(111) also confirm that both the symmetry of the
substrate and of the molecular conformation have a strong influence on the
induced spin polarization. Our finding may give valuable insights for further
engineering of spin filtering devices through single molecular orbitals.
