Giant orbital Hall effect and field-free magnetization switching in rare-earth samarium/platinum metallic heterostructures

Orbital current refers to the flow generated by transmitting the orbital angular momentum of electrons. Compared to spin current, orbital current exhibits distinct advantages, including lower critical current density for magnetization switching, longer propagation distances, and enhanced stability in high-temperature environments. However, the effective utilization of orbital currents remains underexplored. This study reports a giant torque efficiency in Sm/Pt metallic heterostructures, enabling highly efficient magnetization switching. Spin-torque ferromagnetic resonance measurements reveal a tenfold enhancement in torque efficiency (ξ = 0.10 ± 0.02) for the Sm/Pt/Py system compared to Pt/Py. This enhancement originates from the dominant contribution of orbital current. Furthermore, the Sm/Pt/Co/Pt heterostructure exhibits a low critical switching current density (Jsw+ < 3.98 × 106 A/cm2), demonstrating a tenfold improvement in switching efficiency over conventional Pt/Co/Pt systems. We have also achieved field-free switching across all tested thicknesses of the Sm. These metallic heterostructures, combining large effective orbital Hall angles, low thermal dissipation, and compatibility with semiconductor integration, hold significant promise for large-scale applications in orbitronic devices.