Enhanced SOT Efficiency in Pt/Co Systems with a NiO Interlayer for SOT-MRAM

To enable spin-orbit torque (SOT) magnetic random-access memory (MRAM) a decrease in the switching current is needed. One method to achieve this is by improving the SOT efficiency. In this work, the interface of Pt/Co systems are modified with NiO in order to study its effect on the damping-like SOT efficiency. The NiO thickness was varied to study its impact on the Pt/Co structure and Co magnetization as well as the antiferromagnetic (AFM) ordering of the interlayer. The results show Co magnetization direction dependence on the NiO thickness. Additionally, annealing was found to not only enhance the perpendicular magnetic anisotropy (PMA) and SOT efficiency, but also to increase intermixing, as evidenced by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). Furthermore, after annealing, an increased thermal stability of the antiferromagnetic ordering of NiO was observed. This prompted considerations about its impact on spin current transport. Despite the observed intermixing, the exact relationship between intermixing and SOT efficiency enhancement remains unclear.