Perpendicular magnetic anisotropy in CoFeB/X (X = MgO, Ta, W, Ti, and Pt) multilayers

Perpendicular magnetic anisotropy (PMA) of CoFeB(1.0 or 0.5 nm)/X(2.0 nm) (X = MgO, Ta, W, Ti, and Pt) multilayers, prepared by magnetron sputtering, has been studied as a function of X layers. The CoFeB/MgO multilayers with Co–O or Fe–O bondings exhibit superior PMA than CoFeB/metal multilayers, whose PMA properties are significantly influenced by the interfacial alloying and metal structures. In contrast to Co/noble-metal multilayers, whose PMA are determined by the interfacial Co atoms, the internal magnetic atoms in CoFeB(1.0 nm)/X(2.0 nm) multilayers make an important contribution to the magnetization normal to the plane and subsequent PMA. These observations and the corresponding mechanisms responsible for the variation of PMA would advance the insight into the PMA in CoFeB-based multilayers and its unique features compared with conventional Co/noble-metal multilayers.

► Perpendicular magnetic anisotropy of CoFeB/MgO arises from the Co(Fe)–O bondings.
► PMA of CoFeB/metal are correlated to the interfacial alloying.
► The crystal structure of metal determines the critical thickness of PMA CoFeB.
► PMA CoFeB remains after annealing at a comparatively low temperature for a short time.