Magnetic proximity effects at a ferrite-5d-metal interface: GGA plus U calculations

We have studied spin polarization due to proximity effect at the interface of nonmagnetic 5d metal (Me = Ta, W, Re, Os, Ir, Pt, and Au) and ferrimagnetic conducting (mixed-valence) magnetite Fe3O4 or insulating maghemite & gamma;-Fe2O3 using ab initio electronic structure calculations. Four variants of chemical bonding at the interfaces have been modeled. It appears that the moments induced are oriented according to spin orientation of Fe ions to which Me atoms are bonded-parallel for the direct Fe-Me exchange path and antiparallel for the Fe-O-Me superexchange. The obtained densities of states show that notable spin polarization occurs only for Me atomic plane at very vicinity of the interface with the ferrite. The effect is maximum -0.2-0.3 & mu;B for Pt, where slightly higher moment is induced by insulating & gamma;-Fe2O3. Among other metals the moment of -0.1 & mu;B is calculated for Ir. The moment induced in Ta is also relatively large -0.1 & mu;B, but with opposite sign and only in the case of Fe-Me bonding. The exceptional behavior of Pt can be associated with the position of its Fermi level (EF) near the edge of the wide 5d band at a local peak of density of states (spin-nonpolarized DOS = 6.2 eV-1 per atom).