Rachel Maizel of Department of Physics, Va Tech

Energy-efficient spintronic devices require a large spin-orbit torque (SOT) and low damping to excite magnetic precession. In conventional devices based on heavy-metal/ferromagnet bilayers, reducing the ferromagnet thickness to ~1 nm enhances the SOT -- but at the detriment of high 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 < 5 x 10^-3 in the FeNi alloy films, despite the steep compositional gradients. Moreover, we also reveal a sizable anti-damping SOT efficiency of up to ~0.1, even without an intentional compositional gradient. Through depth-resolved x-ray diffraction, we identify a lattice strain gradient as the key source of symmetry breaking, which can produce a greater SOT than compositional asymmetry. Our findings provide fresh insights into damping and SOTs in single-layer ferromagnets for power-efficient spintronic devices.

Biography:

Address:Department of Physics, Virginia Polytechnic Institute, Blacksburg, Virginia, United States