Emergence of considerable thermoelectric effect due to the addition of an underlayer in Pt/Co/Pt stack and its application in detecting field free magnetization switching

Abstract

Application of sufficient lateral current to a heavy metal (HM) can switch the perpendicular magnetization orientation of an adjacent ferromagnetic layer through spin–orbit torques (SOTs). The choice of the HM and its arrangement plays a major role for the SOT induced magnetization switching in magnetic heterostructures. Generally, thin Ta is used as an underlayer to the HM layer for better adhesion and smoothness of the HM layer. Here, we show that Ta addition to the asymmetric stack Pt/Co/Pt gives rise to several compelling effects, viz., thermoelectric effects [particularly, anomalous Nernst effect (ANE)], and enhanced perpendicular magnetic anisotropy which was negligible in a Pt/Co/Pt stack. For this Ta/Pt/Co/Pt stack, the antidamping-SOT values are evaluated after carefully removing the contribution from the ANE and it is found to match the AD-SOT of the Pt/Co/Pt stack. We have observed current-induced field-free magnetization switching Ta/Pt/Co/Pt stack with Co thickness gradient. Furthermore, we have utilized the thermoelectric effects to develop a technique to detect the field-free magnetization switching. This technique detects the second harmonic ANE signal as a reading mechanism. Using ANE symmetry with the applied current, the switching can be detected in a single current sweep which was corroborated to the conventional DC Hall method.