Vertically graded FeNi alloys with low damping and a sizeable spin-orbit torque

Rachel E. Maizel; Shuang Wu; Purnima P. Balakrishnan; Alexander J. Grutter; Christy J. Kinane; Andrew J. Caruana; Prabandha Nakarmi; Bhuwan Nepal; David A. Smith; Youngmin Lim; Julia L. Jones; Wyatt C. Thomas; Jing Zhao; F. Marc Michel; Tim Mewes; Satoru Emori

doi:10.1117/12.3029197

4 October 2024 Vertically graded FeNi alloys with low damping and a sizeable spin-orbit torque

Rachel E. Maizel, Shuang Wu, Purnima P. Balakrishnan, Alexander J. Grutter, Christy J. Kinane, Andrew J. Caruana, Prabandha Nakarmi, Bhuwan Nepal, David A. Smith, Youngmin Lim, Julia L. Jones, Wyatt C. Thomas, Jing Zhao, F. Marc Michel, Tim Mewes, Satoru Emori

Author Affiliations +

Proceedings Volume 13119, Spintronics XVII; 131190L (2024) https://doi.org/10.1117/12.3029197
Event: Nanoscience + Engineering, 2024, San Diego, California, United States

Abstract

Energy-efficient spintronic devices require the following two criteria: (1) a large spin-orbit torque (SOT) and (2) low damping to excite magnetic precession with low current input. Conventional ferromagnet/nonmagnetic-metal bilayers can obtain sizeable SOTs; however, this comes at the expense of drastically increasing the damping. Because the origin or the transmission of spin is interfacial in nature, the ferromagnetic layer must be restricted to ∼1nm in thickness to see substantial SOTs. Here, we present an alternative approach to producing sizeable SOTs that allows for a thicker ferromagnetic layer maintaining low damping. Instead of relying on a single interface, we continuously break the bulk inversion symmetry with a vertical compositional gradient of two ferromagnetic elements: Fe with low intrinsic damping and Ni with sizable spin-orbit coupling. We find low effective damping parameters of α_eff < 5 × 10⁻³ in the FeNi alloy films, despite the steep compositional gradients. Moreover, we reveal a sizable anti-damping SOT efficiency of θ_AD ≈ 0.05, even without an intentional compositional gradient. Through depth-resolved x-ray diffraction, we identify a lattice strain gradient as crucial symmetry breaking that underpins the SOT. Our findings provide fresh insights into damping and SOTs in single-layer ferromagnets for power-efficient spintronic devices.

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Rachel E. Maizel, Shuang Wu, Purnima P. Balakrishnan, Alexander J. Grutter, Christy J. Kinane, Andrew J. Caruana, Prabandha Nakarmi, Bhuwan Nepal, David A. Smith, Youngmin Lim, Julia L. Jones, Wyatt C. Thomas, Jing Zhao, F. Marc Michel, Tim Mewes, and Satoru Emori "Vertically graded FeNi alloys with low damping and a sizeable spin-orbit torque", Proc. SPIE 13119, Spintronics XVII, 131190L (4 October 2024); https://doi.org/10.1117/12.3029197

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