Effect of stack structure on damping-like spin–orbit torque efficiency in RuO₂/<i>α</i>-WTa/CoFeB/MgO and RuO₂/(Cr, V)/<i>α</i>-WTa/CoFeB/MgO systems

Abstract Magnetic and spin–orbit torque (SOT) properties of systems with RuO 2 /(SHM: W, WTa)/CoFeB/MgO/Ta and RuO 2 /(NM: Cr, V)/WTa/CoFeB/MgO/Ta and the effect of stack structure on damping-like SOT efficiency ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ξ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">DL</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) are investigated. We observed enhancement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ξ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">DL</mml:mi> </mml:mrow> </mml:msub> </mml:math> in the thin SHM thickness region and perpendicular magnetization of the CoFeB layer. Observed enhancement in the effective spin Hall conductivity in the insertion of the thin NM layer indicates the importance of careful optimization in the stack structure. Signs of orbital Hall conductivity should be the same to observe an enhancement of SOT efficiency, whether the sign of spin Hall conductivity is positive or negative.