Interlayer Exchange Coupling and Perpendicular Magnetic Anisotropy in Co Fe B /MgO/Co Fe B Tunnel Junction Structures

We fabricated a series of Co 40 Fe 40 B 20 (1.2 nm)/MgO(x nm)/Co 20 Fe 60 B 20 (1.2 nm), x = 0.9-1.5, by sputtering and found the presence of the interlayer-exchange-coupling (IEC), as a function of the thickness of MgO spacer, and perpendicular magnetic anisotropy (PMA) after post annealing at 225°C. The coupling strength and sign (corresponded to parallel or antiparallel coupling), which were characterized by the minor loop shift, varied depending upon MgO layer thickness. In addition, the anisotropy energy constant (K u ) and the exchange coupling energy (J) show inverse relation as the annealing temperature varies in the range of 225°C-370°. The anisotropy constant increases as temperature increases while the exchange coupling decreases from ferromagnetic to antiferromagnetic as temperature increases. This effect seems to be consistent with the recent report of a theoretical calculation based on the orange peel model. A comparison between the experimental results and the theoretical model will be given.