Large spin Hall effect and increase in perpendicular magnetic anisotropy in artificially synthesized amorphous W/Hf multilayer/CoFeB system

We studied the spin-Hall effect and perpendicular magnetic anisotropy in W/Hf multilayer/CoFeB/MgO and W80Ta20/Hf multilayer/CoFeB/MgO systems and compared them with those in the beta-W/CoFeB/MgO system. From the cross-sectional high-resolution transmission electron microscopy images, (i) the amorphous structure of W/Hf and W80Ta20/Hf multilayers, (ii) the flat interface between heavy metals and CoFeB, and (iii) highly (100) texture of MgO (1.0nm) on CoFeB were observed in those multilayer systems. A higher spin-Hall effect and enhancement of perpendicular magnetic anisotropy in the W/Hf multilayer/CoFeB/MgO system can be achieved compared to the beta-W/CoFeB/MgO system. In addition, we found that the resistivity in amorphous W/Hf multilayers is low compared to that in beta-W. These results suggest that the artificially synthesized multilayer system is one of the avenues for realizing the heavy metal with a large spin-Hall effect and low resistivity.