Understanding tunneling magnetoresistance during thermal annealing in MgO-based junctions with CoFeB electrodes

The competition between the interface crystallization and diffusion processes, their influence on the onset of symmetry-filtering coherent tunneling of Δ1 band electrons in the MgO-based magnetic tunnel junctions is investigated. Systematic study of the transport and magnetoresistance during thermal annealing of these junctions shows a unique behavior of the tunneling conductance in the parallel state. The optimal annealing time for achieving giant tunneling magnetoresistance at different temperatures is determined. The evolution of magnetoresistance consists of three distinct regions, responsible by different contributions from CoFeB electrodes and the MgO barrier. The whole phenomenon can be understood through an empirical model based on the Landauer tunneling picture. © 2010 The American Physical Society.