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Interfacial Atomic-asymmetry Induced z-spin and Enhanced Spin–Orbit Torque for All-Electrical Magnetization Manipulation
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DOI：10.1016/j.mtphys.2026.102113.png)
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Abstract
En 中文
The ever-growing demand for high-density and low-power magnetic random-access memory (MRAM) stimulates intensive efforts toward all-electrical manipulation of perpendicular magnetization through spin orbit torque (SOT). Although the perpendicularly magnetized W/CoFeB/MgO that possesses high-density potential is compatible to the back-end-of-line processes, field-free switching via SOT, while maintaining CMOS compatibility and wafter-level uniformity, remains challenging. Here, a robust field-free switching (FFS) with enhanced SOT and perpendicular anisotropy in β-W/CoFeB heterostructures are demonstrated through interfacing with atomically-asymmetric layer of Gd100-xPtx between β-W and CoFeB. FFS is observed over composition range of x = 20–50 and FFS ratio peaks at x=30 (Gd70Pt30) with a value of 84%. Ab Initio Random Structure Searching reveals an atomic-level asymmetry in the interface-confined Pm′ phase of Gd70Pt30 that is able to generate out-of-plane spin polarization (z-spin) and induces FFS. Thickness-dependent measurements show that the effective perpendicular anisotropy energy Keff first increases by a factor of ∼3.5 at 0.3 nm Gd70Pt30 and then decreases until the PMA vanishes as Gd70Pt30 ≥ 0.6 nm. FFS occurs over Gd70Pt30 thickness of 0.2-0.5 nm, where PMA is maintained. Moreover, an 85% enhancement of the y-spin Hall conductivity and a σz/σy of over 20% are observed as the Gd70Pt30 thickness varies. Spin-relaxation analysis attributes the y-spin components to a Dyakonov–Perel-like mechanism, evidenced by the deviation from the conventional proportional scaling between spin and momentum relaxation rates. The significantly enhanced y-spin works synergistically with the sizable z-spin, resulting in a high SOT efficiency that accounts for the observed low switching current density (∼1×107 A/cm2) and improved FFS ratio (up to 90%). The simultaneous achievements of improved Keff, enhanced σy and sizable σz offers a promising pathway towards high-density and low-power SOT-MRAM applications.
Keywords:
spin-orbit torque
perpendicular magnetic anisotropy
field-free switching
GdPt alloy
spin Hall conductivity
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