Spin-orbit torque (SOT) switching devices fabricated by combining van der Waals (vdW) based semiconducting ferromagnets (FMs) and Weyl semimetal (WSMs) are appealing because of electric field-controlled magnetism and unconventional charge to spin conversion, which can be exploited for modular memory and logic devices. For instance, the vdW based FM semiconductors, such as Cr2Ge2Te6 (CGT), offer us the opportunity to study SOT devices where electric field-controlled magnetism can be used for enhanced device functionalities1. Also, we have recently shown that field-free deterministic switching of perpendicular magnet can be obtained by utilizing the unconventional spin orbit torque in WTe22. In SOT switching devices, the electrical readout of the semiconducting FM layer is essential for device functionality. Electrical detection of magnetization in conventional insulating/ semiconducting ferromagnet (FM) is routinely achieved by utilizing the spin hall effect generated by the adjacent heavy metal layer3. The electrical readout of magnetization in 2D semiconducting FM has been demonstrated by coupling Cr2Ge2Te6 with heavy metals4 and topological insulators5. However, few reports have shown electrical detection in a vdW based semimetal/FM-semiconductor heterostructures. As shown in Fig. 1, our initial measurements have demonstrated electrical detection of magnetization in Cr2Ge2Te6 by measuring the anomalous Hall resistance in WTe2/CGT bilayers. On the same device, the resistance of individual CGT is more than 100 times higher than the resistance of the bilayer structure as plotted in Fig .2, therefore most of the current is flowing through the WTe2 layer. We will present detailed measurements, which are required to understand the observed anomalous Hall effect induced at the interface in WTe2/CGT bilayer systems. 
**References** 1. I. A. Verzhbitskiy, H. Kurebayashi and H. Cheng, Nat. Electron., Vol. 3, p.460 (2020).
2. IH. Kao, R. Muzzio and H. Zhang, Nat. Mater. (2022).
3. A. S. Ahmed, A. J. Lee and N. Bagués, Nano Lett., Vol. 19(8), p.5683 (2019).
4. V. Gupta, T. M. Cham and G. M. Stiehl, Nano Lett., Vol. 20(10), p.7482 (2020).
5. V. Gupta, R. Jain and Y. Ren, arXiv:2206.02537 (2022). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/182b981c0bb3b37d7f6affa4f7e62a49.png)

Electrical detection of magnetization of a layered semiconducting ferromagnet using WTe2

Abstract Body: Spin-orbit torque (SOT) driven deterministic control of the magnetization state of a magnet with perpendicular magnetic anisotropy (PMA) is key to next-generation spintronic applications including non-volatile, ultrafast, and energy-efficient data storage devices1-3. But field-free deterministic switching of perpendicular magnetization remains a challenge because it requires an out-of-plane anti-damping torque, which is not allowed in conventional spin source materials such as heavy metals (HM)1-3 and topological insulators4 due to system symmetry. The exploitation of low-crystal symmetries in emergent quantum materials offers a unique approach to achieve spin-orbit torque with unconventional form5,6. Here, we report the first experimental realization of field-free deterministic magnetic switching of a perpendicularly polarized van der Waals (vdW) magnet employing an out-of-plane anti-damping SOT generated in layered WTe2 which is a low-crystal symmetry quantum material. The numerical simulations confirm that out-of-plane antidamping torque in WTe2 is responsible for the observed magnetization switching in the perpendicular direction. 1. Miron, I. M. et al. Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection. Nature 476, 189-193, (2011). 2. Liu, L. et al. Spin-Torque Switching with the Giant Spin Hall Effect of Tantalum. Science 336, 555-558, (2012). 3. Liu, L. et al. Current-Induced Switching of Perpendicularly Magnetized Magnetic Layers Using Spin Torque from the Spin Hall Effect. Physical Review Letters 109, 096602, (2012). 4. Mellnik, A. R. et al. Spin-transfer torque generated by a topological insulator. Nature 511, 449-451, (2014). 5. MacNeill, D. et al. Control of spin-orbit torques through crystal symmetry in WTe2/ferromagnet bilayers. Nature Physics 13, 300-305, (2017). 6. Xue, F. et al. Unconventional spin-orbit torque in transition metal dichalcogenide--ferromagnet bilayers from first-principles calculations. Physical Review B 102, 014401, (2020).

Deterministic Switching of a Perpendicularly Polarized Magnet Using Unconventional Spin-Orbit Torques in WTe2

Manipulation of the magnetization state of spintronic devices can be achieved by spin-orbit torque (SOT). SOT can be induced by Rashba effect1 or Spin Hall effect2, which are both originated from the spin-orbit (SO) coupling. Therefore, to enhance SOT, materials with strong SO coupling are favored. Weyl semimetals are predicted to be a good candidate for achieving an efficient charge to spin interconversion driven by spin-galvanic effect3. Crystalline Weyl semimetals (e.g., WTe2) also provide an exciting possibility of generating out-of-plane (OOP) anti-damping SOT. The presence of strong OOP anti-damping SOT in WTe2/Py heterostructure, originated from the broken 2-fold rotational symmetry at the interface of WTe2, has been demonstrated by spin-torque ferromagnetic resonance4. Unlike conventional heavy metals such as Pt and Ta that only allow in-plane AD SOT, WTe2 can be more efficient for perpendicular magnetization switching. The 2D ferromagnet Fe3GeTe2 (FGT) has been reported to possess strong perpendicular anisotropy at temperatures below TC ~ 230 K5. Anomalous Hall effect can be utilized to monitor the magnetization state of FGT flake during the switching measurements. SOT switching of perpendicular magnetization has been realized in Pt/FGT semi van der Waals (vdW) heterostructure6-7. However, SOT switching in a complete vdW heterostructure still needs to be demonstrated to fill the gap. As shown in Fig.1, we demonstrated SOT switching of perpendicular magnetization in WTe2/FGT vdW heterostructure, and the chirality of SOT switching was found to switch with the direction of the in-plane field. The current density threshold is plotted in Fig.2 as a function of temperature, where the magnitude required for switching is one order smaller than the previously reported value in conventional heavy metal system Pt/FGT6.References: 1. I. M .Miron, G. Gaudin and S. Auffret, Nat. Mater., Vol. 9, p.230 (2010) 2. K. Ando, S. Takahashi and K. Harii, Phys. Rev. Lett., Vol. 101, p.036601 (2008) 3. A. Johansson, J. Henk and I. Mertig, Phys. Rev. B, Vol. 97, p. 085417 (2018) 4. J. Jiang, F. Tang and X. C. Pan, Phys. Rev. Lett., Vol. 115, p.166601 (2015) 5. D. MacNeill, G. M. Stiehl and M. H. D. Guimarães, Nat. Phys., Vol. 13, p. 300 (2017) 6. M. Alghamdi, M. Lohmann and J. Li, Nano Lett., Vol. 19, p.4400 (2019) 7. X. Wang, J. Tang and X. Xia, Sci. Adv., Vol. 5, p.eaaw8904 (2019)

Efficient spin-orbit torque in vdW heterostructure of 2D itinerant ferromagnet and Weyl semimetal

FOD: Spin Transport

technical paper

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Electrical detection of magnetization of a layered semiconducting ferromagnet using WTe2

Deterministic Switching of a Perpendicularly Polarized Magnet Using Unconventional Spin-Orbit Torques in WTe2

Efficient spin-orbit torque in vdW heterostructure of 2D itinerant ferromagnet and Weyl semimetal

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