Large magnetoresistance in Fe/MgO/FeCo(001) epitaxial tunnel junctions on GaAs(001)

We present tunneling experiments on Fe(001)/MgO(20 Angstrom)/FeCo(001) single-crystal epitaxial junctions of high quality grown by sputtering and laser ablation. Tunnel magnetoresistance measurements give 60% at 30 K, to be compared with 13% obtained recently on (001)-oriented Fe/amorphous-Al2O3/FeCo tunnel junctions. This difference demonstrates that the spin polarization of tunneling electrons is not directly related to the density of states of the free metal surface-Fe(001) in this case-but depends on the actual electronic structure of the entire electrode/barrier system. (C) 2001 American Institute of Physics.