May 2025
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Recently, unconventional spin-orbit torques (SOTs) with tunable spin generation open new pathways for designing novel magnetization control for cutting-edge spintronics innovations. A leading research thrust is to develop field-free deterministic magnetization switching for implementing scalable and energy favorable magnetic recording and storage applications, which have been demonstrated in conventional ferromagnetic and antiferromagnetic material systems. Here we extend this advanced magnetization control strategy to chiral antiferromagnet Mn3Sn using spin currents with out-of-plane canted polarization generated from low-symmetry van der Waals (vdW) material WTe2. Numerical calculations suggest that damping-like SOT of spins injected perpendicular to the kagome plane of Mn3Sn serves as a driving force to rotate the chiral magnetic order, while the field-like SOT of spin currents with polarization parallel to the kagome plane provides the bipolar deterministicity to the magnetic switching. We further introduce scanning quantum microscopy to visualize nanoscale evolutions of Mn3Sn magnetic domains during the field-free switching process, corroborating the exceptionally large magnetic switching ratio up to 90%. Our results highlight the opportunities provided by hybrid SOT material platforms consisting of noncollinear antiferromagnets and low-symmetry vdW spin source materials for developing next-generation, transformative spintronic logic devices.
![Moiré superlattices of tDT CrI3
a Left: Moiré superlattice structure of a small-twist-angle tDT CrI3. Only the two layers of Cr atoms adjacent to the twisted interface are shown for visual clarity. Cr atoms belonging to the top and bottom CrI3 layers are labeled in blue and red colors, respectively. Right: Schematic of rhombohedral (AB) and monoclinic (AB’) stacking driven FM and AFM orders in the magnetic ground state of small-twist-angle tDT CrI3. Magnetic moments carried by the middle two CrI3 monolayers are ferromagnetically or antiferromagnetically coupled depending on the local interlayer exchange interaction JR and JM at the twisted interface. The blue and red arrows represent the local magnetic moment carried by Cr atoms (blue and red balls) at individual layers. The yellow balls represent the I atoms and the black dashed lines highlight the twisted interface. b SAED patterns of the fifth-order Bragg peaks of a ~0.8° tDT CrI3 device (blue and red rectangles) from a surveyed sample area of ~850 nm ×\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times$$\end{document} ~ 850 nm. c BF-TEM real-space image of a sample region showing the characteristic hexagonal superlattice structure in the ~0.8° tDT CrI3 device. The scale bar is 25 nm.](https://www.researchgate.net/publication/382079622/figure/fig1/AS:11431281259361529@1720493397719/Moire-superlattices-of-tDT-CrI3-a-Left-Moire-superlattice-structure-of-a_Q320.jpg)
![NV spin relaxometry measurements of spin fluctuations in 0.15° tDT CrI3
a Zoomed-in view of a magnetization map measured on a selected sample area (400 nm ×\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times$$\end{document} 400 nm) of the 0.15° tDT CrI3 device, showing co-existing FM and AFM domains. b Schematic of NV spin relaxometry measurements to probe spin fluctuations of local FM and AFM states in a proximal sample. The blue and red arrows represent local magnetic moments forming spontaneous AFM and FM orders. Noncoherent magnetic noise arising from FM or AFM spin fluctuations at the NV ESR frequencies fESR will drive NV spin transitions from the ms = 0 to the ms = ±\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}1 state, resulting in enhanced NV relaxation rate. c Temperature dependence of NV spin relaxation rate Γ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Gamma$$\end{document} measured when the NV center is positioned right above the FM and AFM domains formed in the 0.15° tDT CrI3 sample. Control measurement results are also presented to characterize the intrinsic NV spin relaxation rate. d 1D NV spin relaxation rate Γ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Gamma$$\end{document} measured along the white dashed lines across the co-existing FM and AFM domains in the 0.15° tDT CrI3 device shown in Fig. 3a. The peak values of Γ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Gamma$$\end{document} measured at 48 K and 58 K occur at the corresponding in-plane lateral positions of AFM and FM domains, respectively.](https://www.researchgate.net/publication/382079622/figure/fig3/AS:11431281259445073@1720493398414/NV-spin-relaxometry-measurements-of-spin-fluctuations-in-015-tDT-CrI3-a-Zoomed-in-view_Q320.jpg)
![Increased Curie temperatures of FM domains formed in small-twist-angle tDT CrI3
a–c Reconstructed magnetization maps of selected sample areas of 0.15° tDT CrI3 (a), 0.25° tDT CrI3 (b), and 15° tDT CrI3 (c) device measured at 38 K. d–f Reconstructed magnetization maps of the same sample areas of the 0.15° tDT CrI3 (d), 0.25° tDT CrI3 (e), and 15° tDT CrI3 (f) device measured at 48 K. Scale bar is 200 nm in a–f. g Temperature dependence of average out-of-plane magnetization m¯z\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\bar{m}}_{{{{{{\rm{z}}}}}}}$$\end{document} of FM domains formed in the selected sample areas of 0.15° tDT CrI3, 0.25° tDT CrI3, and 15° tDT CrI3 device. Inset shows a zoomed-in view of the magnetic curves around transition temperatures. h Histograms of the obtained magnetic transition temperatures of individual FM domains formed in selected sample areas of 0.15° tDT CrI3, 0.25° tDT CrI3, and 15° tDT CrI3 sample shown in a–f.](https://www.researchgate.net/publication/382079622/figure/fig4/AS:11431281259409106@1720493398655/Increased-Curie-temperatures-of-FM-domains-formed-in-small-twist-angle-tDT-CrI3-a-c_Q320.jpg)
![Quantum imaging of SOT‐driven chiral spin rotation in an Mn3Sn/Pt device. a) Schematic illustration of the measurement geometry for SOT‐driven chiral spin rotation in Mn3Sn. Electric charge current flowing in the metal layer generates spin currents with polarization s along the y‐axis. Above the critical current density, the generated spin current drives a continuous rotation of the magnetic octupoles of Mn3Sn with the kagome planes perpendicular to s. The orange arrow represents the applied electric current, and the green arrows represent the polarization of the spin currents generated. b) Calculated time dependence of the weak ferromagnetic moment parallel to the [112¯0]$[11\bar 20]$ axis (m[112¯0]${m_{[11\bar 20]}}$) for Mn3Sn/Pt. The electric current is applied from t = 5 ns to t = 35 ns and the kagome plane is set to be perpendicular to the spin polarization axis s in the presented simulations. c,d) Measured normalized Hall resistance (RH − <RH>)/RAHE as a function of pulse number (N) for write current amplitudes of 2 mA (c) and 44 mA (d). <RH> is the average of RH and RAHE is the zero‐field Hall resistance. e,h) 2D images of Bz measured after applying the first current pulse (N = 1) with magnitudes of 2 mA (e) and 44 mA (h), respectively. f,g) SOT‐induced variation of the stray field ΔBz recorded after applying a 2 mA current pulse 10 (f) and 20 (g) times. i,j). SOT‐induced variation of stray field ΔBz recorded after applying a 44 mA current pulse 10 (i) and 20 (j) times. For (e–j), the black dashed lines mark the boundary of the patterned Mn3Sn/Pt Hall cross, and the scale bar is 2.5 µm.](https://www.researchgate.net/publication/359457636/figure/fig4/AS:11431281173339024@1688844009786/Quantum-imaging-of-SOT-driven-chiral-spin-rotation-in-an-Mn3Sn-Pt-device-a-Schematic_Q320.jpg)
