Giant Damping-Like Torque Efficiency via Synergistic Spin Hall and Enhanced Orbital Hall Effects.

Current-induced spin-orbit torque has emerged as a promising method for achieving energy-efficient magnetization switching in advanced spintronic devices. Over the past few decades, researchers have primarily focused on enhancing spin current generation through the spin Hall effect, relying predominantly on the spin degree of freedom (DoF) of the electron, while neglecting its orbital counterparts. In this work, by leveraging both spin and orbital DoFs, we have enhanced net damping-like torque efficiency (ξDLE) by 1.7 times compared to the sample with only Pt (1.5 nm) as the spin Hall layer. Further, we introduced a thin NiW seed layer to enhance the torque efficiency by 2.5 times. Moreover, we disentangled the spin and orbital contributions to the net ξDLE in a nonmagnet/ferromagnet heterostructure by systematically investigating the torque efficiencies calculated from different heterostructures. Further, the Pt thickness optimization to efficiently harness the spin and orbital Hall effect in the Ru/Pt heterostructure showed a 4-fold enhancement in the ξDLE. Our study underscores the potential of utilizing both the spin Hall effect and the enhanced orbital Hall effect achieved by seed layer engineering to drive next-generation spintronics, combining high-density integration with improved energy efficiency.