Perpendicular Magnetic Anisotropy at Co/AlOx Interface

Magnetic measurements have been performed on thin films with structures Ta/Pt/Co/AlO_x to investigate the dependence of the perpendicular magnetic anisotropy induced at the Co/AlO_x interface on both Co thickness and annealing temperature. The choice of the capping layers to protect the oxide layer is shown to be important. The interfacial anisotropy increases strongly with increasing annealing temperature, from 0.7 to 1.4 erg/cm² , without a major change of the volume anisotropy (11 10⁶ erg/cm³). As a consequence, the critical Co thickness (at which the magnetic moment switches from perpendicular to inplane orientation), increases a lot with annealing and reaches values larger than 3 nm after annealing at 375degC.