Perpendicular magnetic anisotropy and its voltage control in MgO/CoFeB/MgO junctions with atomically thin Ta adhesion layers

We study the perpendicular magnetic anisotropy (PMA) and the voltage-controlled magnetic anisotropy (VCMA) effect in MgO/Ta/CoFeB/MgO junctions. A few monolayers (3-5 angstrom) of Ta acts as an adhesive layer, allowing for the formation of flat and ultrathin (similar to 10 angstrom) CoFeB films with large PMA on top of MgO. In the MgO/Ta/CoFeB/MgO junctions, the diffusion of Ta to the upper CoFeB/MgO interface is effectively eliminated, and superior thermal stability up to 400 degrees C is demonstrated. Detailed nanostructural analyses reveal the appearance of Co-Fe compositional variation in the CoFeB layer associated with the insertion of Ta layer, which explains the observed changes in PMA and VCMA. Our results will facilitate the development of VCMA-based memory devices and also pave the way toward controlling the magnetic and electric properties of CoFeB thin films through subnanometer-scale compositional modulation. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study shows that Ta layer in MgO/Ta/CoFeB/MgO junctions can enhance the PMA of magnetic films and eliminate the diffusion of Ta, leading to superior thermal stability and the release of VCMA effect. In addition, the Co-Fe compositional variation in CoFeB layer associated with Ta insertion is related to the changes in PMA and VCMA.