▎ 摘　　要

We investigate the unusual features of the proximity effect in graphene-based ferromagnet/superconductor (F/S) heterostructures. We show that, for a weakly doped ferromagnetic graphene with an exchange energy h exceeding its Fermi energy E-F, the Andreev reflection of massless Dirac fermions at the FS interface is accompanied with a Klein tunneling through an exchange field p-n barrier between two spin-split conduction and valence subbands. This spin Andreev-Klein process leads to an anomalous exchange-field-induced increase of the amplitude of Andreev reflection which has significant consequences for the subgap conductance and the shot noise power of an SF junction. For h > E-F, we find that the exchange field enhances the subgap conductance to reach a maximum value which is greater than the corresponding value for non-ferromagnetic structure at bias voltages eV < Delta/root 2. We further demonstrate that, due to the spin Andreev-Klein process, the Josephson coupling in a ferromagnetic graphene Josephson junction can be long-ranged, and that it survives at very large exchange fields h >> E-F. The possibility for transitions between 0 and pi Josephson coupling by varying the doping of the ferromagnetic contact is also demonstrated. (C) 2009 Elsevier Ltd. All rights reserved.