  Application of sufficient lateral current to a heavy metal (HM) can switch
the perpendicular magnetization orientation of adjacent ferromagnetic layer
(FM) 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. Here, in asymmetric Pt/Co/Pt heterostructures,
anti-damping (AD) SOT prevails. Ta addition to this stack (Ta/Pt/Co/Pt) give
rise to several compelling effects viz. competing spin currents (due to
opposite spin-Hall angles of adjacent Ta and Pt layers), significant AD-SOT,
thermoelectric effects (particularly, anomalous Nernst effect (ANE)), and
enhanced perpendicular magnetic anisotropy. For this Ta/Pt/Co/Pt stack, the
AD-SOT values are stabilized to that of the Pt/Co/Pt stack, which is
significant than what is expected for a stack with competing spin currents.
Current-induced field-free magnetization switching was absent in uniformly
grown Ta/Pt/Co/Pt stack. It was observed that a thickness gradient is essential
to assist the field-free magnetization switching in these heterostructures.
Further, the thermoelectric effects are utilized 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.
