Negative spin polarization of the Fe3O4/-Al2O3 interface measured by spin-resolved photoemission

The discovery of giant magnetoresistance in Fe/ Cr multilayers 1 has been followed by a large research effort for almost two decades aiming at developing new materials suitable for spintronics. The interest of a given material is mainly expressed by its spin polarization P =N↑ �N↓ /N↑ +N↓, N↑ N↓ standing for majority spin minority spin electron density of states at the Fermi level. This property is particularly important for magnetic tunnel junctions stacks of two magnetic electrodes separated by a thin insulating layer. 2 Indeed, the tunnel magnetoresistance TMR, corresponding to the variation of resistance between parallel and antiparallel configurations of the electrode magnetizations, is given in a simple view by the Julliere formula: 3 TMR =2 P1P2 / 1� P1P2, P1 and P2 being the spin polarizations of the two electrodes. Magnetite Fe3O4 is thus expected to be an interesting electrode material, for band structure calculations predict a half metallic behavior P = �100%, the con