Magnetotransport in epitaxial magnetic tunnel junctions is investigated while varying the density of dislocations in the MgO barrier. Fe-V alloys with variable composition and lattice mismatch with MgO are used as electrodes. The reduction in the dislocation density was probed by reflection high-energy electron diffraction and high-resolution electron microscopy. Spin-resolved photoemission together with first-principles calculations were used to study the $\Delta$ bands in the alloys. Although their polarization decreases upon alloying, the tunnel magnetoresistance is enhanced for low V content as a consequence of the better structural coherency. Our results demonstrate the direct relation between the density of dislocations in the epitaxial barrier and the tunnel magnetoresistance amplitude.

• Received 4 June 2010

DOI:https://doi.org/10.1103/PhysRevB.82.092405