Magnetic tunnel junctions with Co-based perpendicular magnetic anisotropy multilayers

Magnetic CoFeB/MgO/CoFeB-based tunnel junctions with perpendicular magnetic anisotropy Co/M multilayers (M=Ni, Pd, Pt) have been investigated as a function of structural and magnetic properties. Magnetometry, ferromagnetic resonance, x-ray diffraction, stress tests, and local electrode atom probe tomography were carried out primarily on Co/Ni multilayers. A statistical design of experiments was conducted to optimize the perpendicular magnetic anisotropy and damping parameter α of these multilayers. Seed layers, thickness, and thickness ratios are all critical to achieve perpendicular behavior. Perpendicular MgO-based magnetic tunnel junctions with Co/Ni and Co/Pd reference and free layers were fabricated and tested. Sharp MR-H switching characteristics were observed for the Co/Pd multilayers, and a somewhat softer transition was observed for the Co/Ni multilayer with a Cu seed, which did not have as high a perpendicular anisotropy. Tunneling magnetoresistance (TMR) values were limited to about 10%, primarily because the fcc-bcc-fcc transition does not promote the “MgO giant TMR” symmetry filtering effect.