Thermally Robust Spin–Orbit Torque Switching in Low‐Resistivity Mo‐Alloyed β‐W Heterostructures

ABSTRACT The beta (β) phase tungsten (W) is a promising spin–orbit torque (SOT) material exhibiting a large spin Hall efficiency with potential for complementary metal‐oxide‐semiconductor (CMOS)‐compatible integration. However, reducing its high electrical resistivity while maintaining thermal robustness remains challenging, particularly for automotive applications requiring robust operation over a wide temperature range. Here, this study reports a strategy to enhance SOT efficiency while reducing longitudinal resistivity ( ρ xx ) and critical current density ( J c ) through molybdenum (Mo) alloying, both theoretically and experimentally, while investigating the thermal robustness of the β‐W‐Mo magnetic heterostructures. This study performs first‐principles calculations to predict a composition‐dependent spin Hall conductivity ( σ SH ) of −1857 (ℏ/e) Ω − 1 cm − 1 in the β‐W‐Mo alloy system. Based on the prediction, this study introduces the W 87.3 Mo 12.7 /CoFeB/MgO/Ta heterostructure exhibiting enhanced SOT efficiency of 0.47, while remaining a low ρ xx of 103.5 µΩ cm, thereby yielding a high σ SH of −2283 (ℏ/e) Ω − 1 cm − 1 (compared to 0.30, 122.3 µΩ cm, and −1479 (ℏ/e) Ω − 1 cm − 1 of β‐W, respectively). These attributes enable a distinct reduction of J c to 15.0 MA cm −2 , compared to 25.0 MA cm −2 of β‐W. Critically, reliable SOT switching persists across the full −50 to +150°C range, positioning β‐W‐Mo alloys as premier candidates for energy‐efficient, low‐resistivity magnetic memory or automotive adoption.