Highly efficient spin current source using BiSb topological insulator/NiO bilayers

Abstract

BiSb is a topological insulator with both giant spin Hall effect and high electrical conductivity, which are important for ultralow power spin-orbit-torque magnetoresistive random access memory. However, when a ferromagnetic (FM) thin film is deposited on top of BiSb, large surface roughness and diffusion of Sb out of the BiSb layer into the FM layer results in a much smaller effective spin Hall angle θ SH eff. In this work, we show that by inserting a NiO layer between BiSb and Co, we can significantly improve θ SH eff of BiSb and induce perpendicular magnetic anisotropy at the NiO/Co interface. We obtained a large θ SH eff = 10.3 for the BiSb bottom layer at the NiO layer thickness of 3 nm, which is comparable to the best of BiSb top layer studied so far. Our study shows that BiSb/NiO bilayers are promising for integration of BiSb to SOT-MRAM.

Spin–Orbit Torques and Spin Hall Magnetoresistance Generated by Twin‐Free and Amorphous Bi0.9Sb0.1 Topological Insulator Films

“…The surface is flatter than previous reports on epitaxial BiSb(0001) with roughness from 0.6 to 1 nm. [19,40,47,59] This low roughness helps to obtain a high-quality interface with the ferromagnetic layer (FM), as required for studying SOTs accurately. Overall, the RHEED, XRD, and AFM measurements demonstrate the successful deposition of twin-free epitaxial Bi 0.9 Sb 0.1 (0001) thin films of the highest quality.…”

Gate Control of Spin–Orbit Torque in a Sputtered Bi2Se3/Ni81Fe19 Device

“…While spin properties in a TI/insulator/ferromagnetic structure have been observed using electrical methods by some research groups, , efficient spin–orbit torque has been rarely reported. Other researchers have inserted antiferromagnetic oxides, such as NiO, and reported enhanced spin Hall angles of 0.2–10.3 and damping-like torques of B DL / j = 12–300 mT/(10 7 A cm –2 ) in a BiSb/NiO/Co/Pt structure. Thus, the improvement attained by inserting an insulation layer at the interface might not be a general solution.…”

Bulk and Surface Electrical Properties of BiSb on Flat and Ion‐Beam Nano‐Patterned InP Substrates

“…[ 38 ] This crystallographic orientation is essential for achieving the very large SHE, probably due to the multiple Dirac cones at this surface. Our observation that ion‐beam patterning changes the dominant orientation of an MBE‐grown BiSb film from (003) to (012) may be helpful in optimizing thin‐film preparation for applications in magnetic random access memory devices [ 38–40 ] and skyrmion‐based devices. [ 41 ]…”

“…Our observation that ion-beam patterning changes the dominant orientation of an MBE-grown BiSb film from (003) to (012) may be helpful in optimizing thin-film preparation for applications in magnetic random access memory devices [38][39][40] and skyrmionbased devices. [41]…”