Effect of Ta Insertion in Reference Layers of MTJs With Perpendicular Anisotropy

We analyze the opportunity of inserting a Ta layer between the polarizing section and the high anisotropy section in the reference subsystem of CoFeB-based tunnel junctions with perpendicular magnetic anisotropy. Using vector network analyzer ferromagnetic resonance, polar Kerr magnetometry, and magnetization dynamics modeling, we deduce the strength of the ferromagnetic interlayer exchange coupling energy J through various thickness of tantalum that impacts on the overall performance of the tunnel junctions. J culminates at 0.44 mJ/m² through 3 Å of Ta, but the Co/Pt properties are then suboptimal. Our methodology can be used to rationally find the performance optimum in the reference layers of perpendicularly magnetized tunnel junctions.