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VIDEO DOI: https://doi.org/10.48448/s9sj-kv10

technical paper

MMM 2022

November 07, 2022

Minneapolis, United States

Enhancing Spin Orbit Torque Efficiency via Orbital Currents

It is of great significance in the memory industry to find a conductive spin current source (SCS) possessing a large damping-like spin-orbit torque efficiency (ξDL) higher than W, for the purpose of realizing a faster and more efficient spin-orbit torque magnetic random-access memory (SOT-MRAM). Among numerous candidates, 5d transition metal Pt is one of the more competitive spin Hall materials for efficiently generating spin-orbit torques (SOTs) in Pt/ferromagnetic layer (FM) heterostructures, due to its high spin Hall conductivity (SHC) and moderate resistivity. However, for a long while with tremendous engineering endeavors, the of Pt and Pt alloys are still limited to ξDL<0.5 . In this work, we report that with proper alloying elements, particularly the 3d transition metals V and Cr with giant orbital Hall effect (OHE), the strength of the high spin Hall conductivity of Pt (σSH~6.45×105 (h-bar/2e) Ω-1 m-1) is observed even in the relatively resistive regime. Especially for the Cr-doped case, an extremely high ξDL~0.9 in a perpendicular magnetized Pt0.69Cr0.31/Co device can be achieved with a moderate Pt0.69Cr0.31 resistivity of ρxx~133 μΩ cm . This sizable SOT efficiency can be attributed to the additional spin current generation from orbital-to-spin current conversion, resulting in the increasing SHC as the Cr concentration in the Pt-Cr alloy increases. Moreover, a low critical SOT-driven switching current density of is also demonstrated, and the damping constant (α) of Pt0.69Cr0.31/CoFeB structure is found to be reduced to 0.052 from the pure Pt/CoFeB case of 0.078. The overall high σSH, giant ξDL, moderate ρxx , and the reduction of α make the Pt-Cr/FM heterostructure promising for versatile extremely low power consumption SOT memory applications.
1. Miron, I.M., et al., Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection. Nature, 2011. 476(7359): p. 189-U88.
2. Liu, L.Q., et al., Current-Induced Switching of Perpendicularly Magnetized Magnetic Layers Using Spin Torque from the Spin Hall Effect. Physical Review Letters, 2012. 109(9).
3. Pai, C.F., et al., Determination of spin torque efficiencies in heterostructures with perpendicular magnetic anisotropy. Physical Review B, 2016. 93(14).
4. Liu, L.Q., et al. Spin-Torque Ferromagnetic Resonance Induced by the Spin Hall Effect. Physical Review Letter, 2011, 106, 036601.
5. Lee, Soogil, et al. "Efficient conversion of orbital Hall current to spin current for spin-orbit torque switching." Communications Physics 4.1 (2021): 1-6.
6. Hu, Chen-Yu, et al. "Toward 100% Spin–Orbit Torque Efficiency with High Spin–Orbital Hall Conductivity Pt–Cr Alloys." ACS Applied Electronic Materials 4.3 (2022): 1099-1108.

Damping-like spin-orbit torque efficiency of PtxCr1-x alloys in Pt-Cr/Co structures.


Transcript English (automatic)

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Lanuakum Longchar and 6 other authors

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