Topological materials have great potential for ultralow power spin-orbit torque (SOT) spintronic devices thanks to their giant spin Hall effect originated from their topological surface states (TSSs). However, the giant spin Hall angle (θSH > 1) is limited to a few chalcogenide-based topological insulators (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 focus on a half-Heusler alloy topological semimetal, YPtBi, to overcome this difficulty. We synthesized YPtBi thin films by using co-sputtering method with YPt and Bi targets while changing the growth temperature. Figure 1 (a) shows the X-ray diffraction (XRD) spectra for YPtBi films grown at various temperature. YPtBi(111) peaks were clearly observed up to 600oC. Figure 1 (b) shows the Bi composition measured by X-ray fluorescence (XRF). Bi composition is stable up to 600oC. These results indicate that YPtBi crystal is stable up to 600oC which is high enough for BEOL process. To evaluate the spin Hall effect for YPtBi, we conducted the second harmonic Hall effect measurements in CoPt/YPtBi heterostructures 1. By controlling the electric conductivity of YPtBi and spin transparency at the CoPt/YPtBi interface, we successfully realized a giant θSH up to 4.1. Figure 2 shows SOT magnetization switching by pulse currents with pulse width of 50 μs to 10 ms under an external magnetic field of 0.5 kOe applied parallel to the current. Thanks to the giant spin Hall effect originated from TSS, small threshold current of about 1×106 A/cm2 was observed, which is one order magnitude smaller than that in heavy metals 2. Our work opens the door to the next generation spin Hall materials with both giant θSH and high thermal stability 3. Acknowledgment: this work was supported by Kioxia corporation. The authors thank Tsuyoshi Kondo of Kioxia corporation for fruitful discussion.

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