High spin-orbit torque efficiency induced by engineering spin absorption for fully electric-driven magnetization switching.

Realizing spin-orbit torque (SOT)-driven magnetization switching offers promising opportunities for the advancement of next-generation spintronics. However, the relatively low charge-spin conversion efficiency accompanied by an ultrahigh critical switching current density (J_c) remains a significant obstacle to the further development of SOT-based storage elements. Herein, spin absorption engineering at the ferromagnet/nonmagnet interface is firstly proposed to achieve high SOT efficiency in Pt/Co/Ir trilayers. The J_c value was significantly decreased to 7.5 × 10⁶ A cm^-2, achieving a maximum reduction of 58% when a 4.0-nm Gd layer was inserted into the Co/Ir interface. A similar trend was observed in the trilayers with various rare metal insertions, suggesting the universality of this approach. Simultaneously, the highest effective spin Hall angle of 0.29 was obtained in the Pt/Co/Gd (4.0 nm)/Ir multilayers, which was approximately three times greater than that obtained in the Pt/Co/Ir trilayer. First-principles calculations together with polarized neutron reflectivity results revealed that spin mixed conductivity can be significantly enhanced due to a spontaneous interfacial CoGd alloy, which is critical for high SOT efficiency. In addition, the deterministic field-free switching polarity can be tuned by introducing Gd insertion. These findings provide a promising pathway for deeply understanding the spin-charge conversion mechanism, and further enable the design of low-consumption spintronic circuits.