Efficient spin current source using a half-Heusler alloy topological semimetal with back end of line compatibility

Abstract

Topological materials, such as topological insulators (TIs), have great potential for ultralow power spintronic devices, thanks to their giant spin Hall effect. However, the giant spin Hall angle (θSH > 1) is limited to a few chalcogenide TIs with toxic elements and low melting points, making them challenging for device integration during the silicon Back-End-of-Line (BEOL) process. Here, we show that by using a half-Heusler alloy topological semi-metal (HHA-TSM), YPtBi, it is possible to achieve both a giant θSH up to 4.1 and a high thermal budget up to 600 °C. We demonstrate magnetization switching of a CoPt thin film using the giant spin Hall effect of YPtBi by current densities lower than those of heavy metals by one order of magnitude. Since HHA-TSM includes a group of three-element topological materials with great flexibility, our work opens the door to the third-generation spin Hall materials with both high θSH and high compatibility with the BEOL process that would be easily adopted by the industry.

Effect of stoichiometry on the spin Hall angle of the half-Heusler alloy topological semimetal YPtBi

“…4(e)]. 20) This implies that the spin Hall effect in YPtBi is robust against the change of its stoichiometry, which is another evidence of the Berry phase origin of the spin Hall effect in YPtBi, and is a technological advantage of this alloy for device applications. This also explains why there is no correlation between the order parameter in Fig.…”

“…Here, perpendicular magnetic anisotropy (PMA) was realized at most of the r values thanks to the flat interface of YPtBi. 20) However, H k eff suddenly drops at r = 0.5 and around r ∼ 1.2. Figure 3(f) shows the r dependence of the surface roughness of the CoPt/YPtBi heterostructures evaluated by atomic force microscopy.…”

“…In our previous work, we showed that the effective spin Hall angle q SH eff of YPtBi is sensitive to its electrical conductivity, which depends on the crystal growth parameters. 20) However, the effect of stoichiometry on the spin Hall angle in this alloy is not well understood. It is well-known that the spin Hall effect in topological insulators, such as Bi 2 Se 3 , depends strongly on stoichiometry, which brought controversy about the value of q SH eff and is a big problem for using topological insulators in realistic spin devices.…”

“…Here, we focus on the half-Heusler alloy topological semimetal (HHA-TSM), YPtBi, 18,19) which has shown both large θ SH (>1) and high thermal stability (600 °C) that are important for the back end of line processes. 20) Although ideal topological half-Heusler alloys are zero-gap topological insulators with no Fermi surface, 18) there are extrinsic carriers due to various crystal defects that make those alloys semimetal with a finite Fermi surface. In our previous work, we showed that the effective spin Hall angle q SH eff of YPtBi is sensitive to its electrical conductivity, which depends on the crystal growth parameters.…”

Effects of post-growth annealing in YPtBi topological semimetal and Co/Pt perpendicular magnetization multilayers

“…) is limited to chalcogenide TIs [12][13][14][15][16][17] with low mp and toxic elements, making them difficult to use in the back end of line process. Recently, we have observed a giant SHE with q SH as high as 7.8 at RT in the half-Heusler alloy topological semimetal (HHA-TSM), YPtBi, [18][19][20] whose giant SHE originates from the intrinsic mechanism (i.e. Berry phase) 21) of its TSSs.…”