Effect of Mo capping layers thickness on the perpendicular magnetic anisotropy in MgO/CoFeB based top magnetic tunnel junction structure

A detailed study of the magnetic characterizations of the top structure MgO/CoFeB/Mo is presented. The samples show strong perpendicular magnetic anisotropy (PMA) when the thickness of CoFeB is 0.9 nm and 1.1 nm. The saturation magnetic moment and interface anisotropy constant are 1566 emu/cm(3) and 3.75 erg/cm(2), respectively. The magnetic dead layer (MDL) is about 0.23 nm in this system. Furthermore, strong capping layer thickness dependence is also observed. The strong PMA of 1.1 nm CoFeB only exists in a Mo cap layer thickness window of 1.2-2 nm. To maintain PMA, the metal layer could not be too thin or thick in these multilayers. The oxidation and diffusion of the metal capping layer should be respectively responsibility for the degradation of PMA in these thin or thick metal capping layer samples.