Structural characterizations of Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions by transmission electron microscopy

We have investigated the structure of Co2MnSi/MgO/Co2MnSi magnetic tunneling junctions with different tunnel magnetoresistance values depending on the in situ annealing temperatures just after the deposition of the upper Co2MnSi electrodes. The nano-beam diffraction patterns indicated that the degree of order of the upper Co2MnSi electrode annealed at 550°C was higher than that of an electrode annealed at 400°C. Moreover, the degree of the L21 order of the upper Co2MnSi electrode annealed at 550°C was even lower than that of the lower Co2MnSi electrode annealed at an almost equal temperature of 600°C. Atomic-scale observation using a high-angle annular dark-field (HAADF) method distinctly showed the existence of the L21-ordered regions in the B2-ordered matrix in the upper Co2MnSi electrode annealed at 400°C.