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Vertically Graded FeNi Alloys with Low Damping and a Sizeable Spin-Orbit Torque



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


Energy-efficient spintronic devices require a large spin-orbit torque (SOT) and low damping to excite magnetic precession. In conventional devices with heavy-metal/ferromagnet bilayers, reducing the ferromagnet thickness to ∼1 nm enhances the SOT but dramatically increases damping. Here, we investigate an alternative approach based on a 10 nm thick single-layer ferromagnet to attain both low damping and a sizable SOT. 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 eff < 5×10−3 in the FeNi alloy films, despite the steep compositional gradients. Moreover, we reveal a sizable anti-damping SOT efficiency of 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.
Physical Review Materials


Magnetism, Thin film, neutron reflectometry, spin orbit torque, metals, spintronics


Maizel, R. , Wu, S. , Balakrishnan, P. , Grutter, A. , Kinane, C. , Caruana, A. , Nakarmi, P. , Nepal, B. , Smith, D. , Lim, Y. , Jones, J. , Thomas, W. , Zhao, J. , Michel, F. , Mewes, T. and Emori, S. (2024), Vertically Graded FeNi Alloys with Low Damping and a Sizeable Spin-Orbit Torque, Physical Review Materials (Accessed July 12, 2024)


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Created June 14, 2024, Updated June 27, 2024