Enhancement of Perpendicular Magnetic Anisotropy Through Fe Insertion at the CoFe/W Interface

Magnetic tunnel junctions (MTJs) based on MgO/CoFeB/W structures are of particular interest for magnetic random access memories due to their high tunnel magnetoresistance, low damping, and stable properties at high annealing temperature. One of the major challenges is to obtain a strong interfacial perpendicular magnetic anisotropy (PMA) for sufficient thermal stability during data storage. Here we investigate magnetic anisotropy energies (MAEs) in the ferromagnet (FM)/W structure with different FM materials and interface insertions. We find that the Fe/W interface exhibits a remarkable PMA, whereas the Co/W interface displays a large in-plane anisotropy, which reduces the PMA in the MgO/CoFeB/W structure. By inserting a thin Fe layer at the CoFe/W interface, the interfacial PMA can be enhanced to 3.34 mJ/m². Microscopic mechanism behind these phenomena is explained with the changes of orbital-resolved MAEs due to the charge redistribution at the interface. These findings pave a new way for the enhancement of PMA and point toward the possibility of achieving high thermal stability in small-node MTJs.