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

Published

October 4, 2024

Author(s)

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

Abstract

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 approximately 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 αeff < 5 × 10−3 in the Fe-Ni alloy films, despite the steep compositional gradients. Moreover, we reveal a sizable antidamping SOT efficiency of |θAD| ≈ 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.

Citation

Physical Review Applied

Volume

22

Issue

4

Pub Type

Journals

Download Paper

https://doi.org/10.1103/PhysRevApplied.22.044052

Local Download

Keywords

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

Citation

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 Fe-Ni Alloys with Low Damping and a Sizeable Spin-Orbit Torque, Physical Review Applied, [online], https://doi.org/10.1103/PhysRevApplied.22.044052, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958189 (Accessed July 19, 2025)