Effect of thickness of MgO, Co-Fe-B, and Ta layers on perpendicular magnetic anisotropy of [Ta/Co_(60)Fe_(20)B_(20)/MgO]_5 muItilayered films

摘要

This study elucidates the magnetic properties of [Ta/Co_(60)Fe_(20)B_(20)/MgO]_5 as functions of thickness of each layer. Its perpendicular magnetic anisotropy (PMA) is found to depend strongly on the thickness of the MgO (t_(MgO)) and Co-Fe-B (t_(CoFeB)) layers. The Ta/CoFeB interface is critical to inducing PMA. A maximum room-temperature (RT) anisotropic energy (K_u~(RT)) of about 1 × 10~6 erg/cm~3 and an anisotropic field (H_k~(RT)) of 4.7 kOe are obtained in the RT-prepared multilayered sample with t_(MgO)=1.0, t_(CoFeB)=l.3, and thickness of layer r_(Ta)=10nm. These values are comparable to the published values for Co_(60)Fe_(20)B_(20) after optimized field annealing. In this investigation, post-annealing has a more complicated effect on PMA in a multilayered structure than in a single or a double Co-Fe-B layer, both of which structure have been examined elsewhere. This result may be explained by the competing effects of the thermal process, which is an improvement of the crystallinity of Co-Fe-B and roughening of the interface.