Influence of annealing on spin-dependent tunneling characteristics of fully epitaxial Co2MnGe/MgO/Co50Fe50 magnetic tunnel junctions

We found that the tunnel magnetoresistance ratio of fully epitaxial Co2MnGe/MgO/Co50Fe50 magnetic tunnel junctions (MTJs) increased discontinuously and significantly from 92% at room temperature (RT) (244% at 4.2 K) for T-a of 475 degrees C to 160% at RT (376% at 4.2 K) for T-a of 500 degrees C, where T-a is the temperature at which the MTJ trilayer was in situ annealed right after deposition of the upper electrode. We also found that the dI/dV versus V characteristics for the parallel and antiparallel magnetization configurations changed discontinuously and markedly with increasing T-a from 475 degrees C or less to 500 degrees C or higher. These significant changes are discussed in terms of a possible change in the spin-dependent interfacial density of states.