Perpendicular magnetic anisotropy (PMA) was achieved in annealed Co2FeAl0.5Si0.5 (CFAS)/MgO-based multilayers with good thermal stability up to 400 degrees C and a large anisotropy energy density K-u over 2.0 x 10(5) J/m(3). The thickness of the full-Heusler CFAS film to maintain PMA is up to 4.8 nm in which the co-existence of disordered A2, ordered B2 and fully ordered L2(1) structures is observed. X-ray photoelectron spectroscopy analysis demonstrates that the origin of the PMA is the hybridization between Co 3d and O 2p orbitals at the CFAS/MgO interface. (C) 2013 Elsevier B.V. All rights reserved.