Irradiation Effects on Perpendicular Anisotropy Spin Orbit Torque Magnetic Tunnel Junctions

We study the impact of irradiation on magnetic tunnel junction (MTJ) films with perpendicular magnetic anisotropy (PMA) and spin orbit torque (SOT) switching using magneto-optical Kerr effect and transmission electron microscopy. Our results show that the thin film stack is robust to gamma ionizing dose up to 1 Mrad(Si) and Ta1+ ion irradiation fluences up to 1012 ions/cm2, showing SOT PMA MTJs are radiation-hard. But, at very high Ta1+ ion irradiation between 1012 - 1014 ions/cm2, reduced coercivity and eventually greatly reduced perpendicular magnetic anisotropy is observed, corresponding with an increase in intermixing of the CoFeB-MgO layers, particularly at the lower CoFeB-MgO interface. These results agree with displacement damage modeling that predicts higher damage in the layers closer to the bottom heavy metal and substrate. Compared to spin transfer torque and in-plane anisotropy MTJs, needing a top-pinned stack, a thicker heavy metal layer, and perpendicular anisotropy that is pinned out of plane by interfaces, all could make SOT PMA MTJs more susceptible to damage at high doses.