Enhanced tunneling magnetoresistance and perpendicular magnetic anisotropy in Mo/CoFeB/MgO magnetic tunnel junctions

Structural, magnetic, and transport studies have been performed on perpendicular magnetic tunnel junctions (pMTJ) with Mo as the buffer and capping layers. After annealing samples at 300'°C and higher, consistently better performance was obtained compared to that of conventional pMTJs with Ta layers. Large tunneling magnetoresistance (TMR) and perpendicular magnetic anisotropy (PMA) values were retained in a wide range of samples with Mo layers after annealing for 2 h at 400'°C, in sharp contrast to the junctions with Ta layers, in which superparamagnetic behavior with nearly vanishing magnetoresistance was observed. As a result of the greatly improved thermal stability, TMR as high as 162% was obtained in junctions containing Mo layers. These results highlight the importance of the heavy-metal layers adjacent to CoFeB electrodes for achieving larger TMR, stronger PMA, and higher thermal stability in pMTJs.