  We created epitaxial magnetic tunnel junctions of FeCo/MgO/EuS on MgO
buffered Si (100). Tunnel magnetoresistance reached up to 64% at 4.2 K. An
unexpected fast drop of magnetoresistance was recorded for MgO thickness above
1 nm, which is attributed to the forced nonspecular conductance across the EuS
conduction band minimum located at the X point, rather than the desired Delta_1
conductance centered around the Gamma point.
