Effects of MgO Thickness and Roughness on Perpendicular Magnetic Anisotropy in MgO/CoFeB/Ta Multilayers**Supported by the National Basic Research Program of China under Grant No 2011CB921804, and the Beijing Key Subject Foundation of Condensed Matter Physics under Grant No 0114023.

Abstract

The dependence of perpendicular magnetic anisotropy (PMA) on the barrier layer MgO thickness in MgO/CoFeB/Ta multilayers is investigated. The results show that the strongest PMA occurs in a small window of about 2–4 nm with the increase of MgO thickness from 1–10 nm. The crystalline degree of MgO and the change of interatomic distance along the out-of-plane direction may be the main reasons for the change of PMA in these multilayers. Moreover, the roughnesses of 2- and 4-nm-thick MgO samples are 3.163 and 1.8 nm, respectively, and both the samples show PMA. These results could be used to tune the magnetic characteristic of the ultra thin CoFeB film for future applications in perpendicular magnetic devices.