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

초록

The beta (beta) 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 (rho xx) and critical current density (J c) through molybdenum (Mo) alloying, both theoretically and experimentally, while investigating the thermal robustness of the beta-W-Mo magnetic heterostructures. This study performs first-principles calculations to predict a composition-dependent spin Hall conductivity (sigma SH) of -1857 (& hbar;/e) Omega- 1 cm- 1 in the beta-W-Mo alloy system. Based on the prediction, this study introduces the W87.3Mo12.7/CoFeB/MgO/Ta heterostructure exhibiting enhanced SOT efficiency of 0.47, while remaining a low rho xx of 103.5 & micro;Omega cm, thereby yielding a high sigma SH of -2283 (& hbar;/e) Omega- 1 cm- 1 (compared to 0.30, 122.3 & micro;Omega cm, and -1479 (& hbar;/e) Omega- 1 cm- 1 of beta-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 beta-W. Critically, reliable SOT switching persists across the full -50 to +150 degrees C range, positioning beta-W-Mo alloys as premier candidates for energy-efficient, low-resistivity magnetic memory or automotive adoption.

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