  The spin dependent properties of epitaxial Fe3O4 thin films on GaAs(001) are
studied by the ferromagnetic proximity polarization (FPP) effect and
magneto-optic Kerr effect (MOKE). Both FPP and MOKE show oscillations with
respect to Fe3O4 film thickness, and the oscillations are large enough to
induce repeated sign reversals. We attribute the oscillatory behavior to
spin-polarized quantum well states forming in the Fe3O4 film. Quantum
confinement of the t2g states near the Fermi level provides an explanation for
the similar thickness dependences of the FPP and MOKE oscillations.
