Adsorbate-induced spin-polarization enhancement of Fe₃O₄(0 0 1)

Using a spin-polarized metastable helium beam, we have investigated the remanent spin polarization at the surface of clean, hydrogen-terminated and benzene-adsorbed Fe₃O₄(0 0 1) thin films prepared on MgO(0 0 1) substrates. For the clean surface, a small negative asymmetry is detected in the ejected electron yields for helium-electron spins aligned parallel and anti-parallel to the sample magnetization direction. This confirms earlier experimental results from less surface-sensitive techniques which show that the spin polarization at the surface of Fe₃O₄(0 0 1) is much reduced from the bulk value and, furthermore, implies that majority-spin states actually dominate at the Fermi level. However, when hydrogen-terminated, the asymmetry is considerably enhanced and positive highlighting the important role that surface adsorption and passivation will play in the development of spintronic materials. This is further demonstrated for the adsorption of the simplest π-conjugated molecule, benzene, at the clean Fe₃O₄(0 0 1) surface where a similar enhancement in the spin polarization is observed, an effect that could prove beneficial to the design and fabrication of organic spintronic devices.