Large Spin-Orbit-Torque Efficiency Generated by Spin Hall Effect in Paramagnetic Co - Ni - B Alloys

Abstract

The spin Hall effect is a major source of spin-orbit torques (SOTs), which allow efficient electrical manipulation of magnetization. So far, the spin Hall effect has been investigated using materials with strong spin-orbit coupling, such as 5d transition metals, and the spin Hall effect in light elements, which results in weak spin-orbit coupling, is often considered to be negligible. Here, we report an efficient spin Hall material that can be realized using 3d transition metals, namely, an amorphous $\mathrm{Co}$-$\mathrm{Ni}$-$\mathrm{B}$ alloy under a paramagnetic state. Despite no heavy elements being used in this material, we estimate the spin Hall angle of $\mathrm{Co}$-$\mathrm{Ni}$-$\mathrm{B}$ alloys to be about 0.10 via harmonic Hall measurements, which is comparable to that of 5d transition metals. A highly efficient spin Hall angle originates from the high-spin Hall conductivity of paramagnetic $\mathrm{Ni}$. We also demonstrate SOT-induced magnetization switching using the spin Hall effect on the $\mathrm{Co}$-$\mathrm{Ni}$-$\mathrm{B}$ alloy with comparable switching current density using a heavy-metal spin Hall material. Our findings provide an approach to realize the coexistence between highly efficient and heavy-element-free SOT-based devices.