Enhancing perpendicular magnetic anisotropy through dead layer reduction utilizing precise control of Mg insertions

Using an ultrathin metallic layer of Mg at the CoFeB|MgO interface has been emerged as an appealing solution to efficiently enhance the tunneling magnetoresistance and thermal stability while reducing the resistance-area product and effective damping of CoFeB films for efficient and low-power dissipated MTJ. However, it is still a great challenge to significantly enhance the perpendicular magnetic anisotropy (PMA) using Mg interlayer in CoFeB|MgO structures and reveal the behind mechanism, for continuously scaling down the MTJ structure. Here, we investigate the effect of ultrathin Mg insertions of 0.2 nm, 0.4 nm and 0.6 nm on PMA at CoFeB|MgO interface for the CoFeB thickness range of 1–1.5 nm and compare the results with an identical structure without insertion. We observed that upon inserting ultrathin Mg layer, the effective anisotropy turned to out-of-plane even for thicker 1.5 nm CoFeB layers which favors in-plane anisotropy without Mg insertion. We also observe a reasonable increase in the interfacial anisotropy energy along with the effective CoFeB thickness for the structures with Mg insertion. The effect that Mg insertion layer helps reducing the dead layer was revealed accounting for the PMA enhancement mechanism. Our results provide a more detailed explanation for the enhancement of PMA through Mg insertion, which may offer a guidance for the development of CoFeB|MgO based MTJ structure with higher thermal stability and lower switching current.