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# Electrical manipulation of a topological antiferromagnetic state

## Abstract

Electrical manipulation of phenomena generated by nontrivial band topology is essential for the development of next-generation technology using topological protection. A Weyl semimetal is a three-dimensional gapless system that hosts Weyl fermions as low-energy quasiparticles1,2,3,4. It has various exotic properties, such as a large anomalous Hall effect (AHE) and chiral anomaly, which are robust owing to the topologically protected Weyl nodes1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16. To manipulate such phenomena, a magnetic version of Weyl semimetals would be useful for controlling the locations of Weyl nodes in the Brillouin zone. Moreover, electrical manipulation of antiferromagnetic Weyl metals would facilitate the use of antiferromagnetic spintronics to realize high-density devices with ultrafast operation17,18. However, electrical control of a Weyl metal has not yet been reported. Here we demonstrate the electrical switching of a topological antiferromagnetic state and its detection by the AHE at room temperature in a polycrystalline thin film19 of the antiferromagnetic Weyl metal Mn3Sn9,10,12,20, which exhibits zero-field AHE. Using bilayer devices composed of Mn3Sn and nonmagnetic metals, we find that an electrical current density of about 1010 to 1011 amperes per square metre induces magnetic switching in the nonmagnetic metals, with a large change in Hall voltage. In addition, the current polarity along the bias field and the sign of the spin Hall angle of the nonmagnetic metals—positive for Pt (ref. 21), close to 0 for Cu and negative for W (ref. 22)—determines the sign of the Hall voltage. Notably, the electrical switching in the antiferromagnet is achieved with the same protocol as that used for ferromagnetic metals23,24. Our results may lead to further scientific and technological advances in topological magnetism and antiferromagnetic spintronics.

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## Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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## Acknowledgements

We thank D. Qu, T. Tomita, Y. Hibino, T. Nozaki and S. Yuasa for discussions, and D. Nishio-Hamane for SEM-EDX measurements. This work is partially supported by CREST (JPMJCR18T3), Japan Science and Technology Agency (JST), through Grants-in-Aid for Scientific Research on Innovative Areas (15H05882 and 15H05883) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, by Grants-in-Aid for Scientific Research (16H06345, 18H03880, 19H00650) and by the New Energy and Industrial Technology Development Organization.

## Author information

Authors

### Contributions

S.N. conceived the project. S.N., K.K., S.M. and Y.O. planned the experiments. T.H., S.M., A.K., T. Nakano and K.Y. prepared and characterized the Mn3Sn multilayered films. K.K. fabricated the Hall bar devices. H.T., T.H., K.K. and S.M. performed the electrical switching measurements. T.H. performed the magneto-transport measurements and A.S. performed the thermoelectric measurements. T. Nomoto and R.A. performed numerical calculations and provided a theoretical explanation. T.H., T. Nomoto, S.M. and S.N. wrote the manuscript. All authors discussed the results and commented on the manuscript.

### Corresponding author

Correspondence to Satoru Nakatsuji.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

Peer review information Nature thanks Kyung-Jin Lee and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

## Extended data figures and tables

### Extended Data Fig. 1 Longitudinal magnetoconductivity measurements for the Mn3Sn thin film.

a, b, Magnetic field dependence of the magnetoconductivity σ(H) − σ(0) of the 40-nm-thick Mn3Sn film under a magnetic field H parallel (top curves) and perpendicular (bottom curves) to the current I at 300 K (a) and 250 K (b). Here σ(0) is the magnetoconductivity at 0 T. c, d, Angular (Θch) dependence of the magnetoconductivity σ(H) − σ(0) of the 40-nm-thick Mn3Sn film at 300 K (c) and 250 K (d). e, Schematic of the experimental setup used for the magneto-transport measurements. To examine the current homogeneity, we employ three pairs of voltage terminals—(V1, V2) and (V3, V4) on the two sides and (V5, V6) on the centre line of the film—for the measurement shown in a. For the measurements shown in bd, the pair (V1, V2) is used.

### Extended Data Fig. 2 Longitudinal MC and planar Hall conductivity measurements for the Mn3Sn thin film.

a, Angular (Φch) dependence of the longitudinal MC Δσ = σ − σ of the 40-nm-thick Mn3Sn film at 250 K. Φch is the in-plane angle between the magnetic field H and the electrical current I. The blue solid line shows the fitting results using equation (2). b, Angular (Φch) dependence of the planar Hall conductivity $${\sigma }_{{\rm{H}}}^{{\rm{PHE}}}$$ of the 40-nm-thick Mn3Sn film at 250 K. The pink solid line shows the fitting results using equation (3). c, Schematic of the measurement setup used for the longitudinal MC and PHE with the pairs of terminals (V1, V2) and (VH1, VH2).

### Extended Data Fig. 3 Large ANE in the Mn3Sn thin film.

Double-logarithmic plot of the anomalous Nernst coefficient |SANE| versus magnetization M for various FMs, for Mn3Sn single crystals at various temperatures (blue solid circles) and for the polycrystalline Mn3Sn thin film at 300 K (red star). The yellow shaded region highlights the empirical scaling law with M. ML, multilayer; N, number of the stacking. Data from ref. 10, Springer Nature.

### Extended Data Fig. 4 Field-induced sign change in transverse thermoelectric conductivity and Hall conductivity of the Mn3Sn thin film.

a, b, Field dependence of the anomalous Nernst coefficient SANE and the Hall resistivity ρH (a) and the transverse thermoelectric conductivity αN and Hall conductivity σH (b) of the the 40-nm-thick Mn3Sn thin film at room temperature. The Seebeck coefficient SSE and the resistivity ρ are also measured at 300 K and found to be constant (SSE = 7.6 μV K−1 and ρ = 290 μΩ cm) in the field sweep measurements below ±4 T. αN is estimated from the electrical conductivity σ = 1, the Hall conductivity σH = −ρH/ρ2, the Seebeck coefficient SSE and the Nernst coefficient SANE using the equation αN = σSANE + σHSSE (Methods). Here, the heat current Q and electrical current I are applied parallel to the film plane and the field is applied along the normal direction (z direction) to the film plane.

### Extended Data Fig. 5 Control of the nodal direction connecting a pair of Weyl points using the magnetic octupole polarization.

af, Cluster magnetic octupole (orange arrow) consisting of the six spins on the kagome bilayer in real space (left) and schematic distributions of the Weyl points near the Fermi energy in momentum space (kxky plane at kz = 0; right) for each magnetic structure of Mn3Sn corresponding to φ = π/6 (a), π/2 (b), 5π/6 (c), −π/6 (d), −π/2 (e) and −5π/6 (f). Red and blue spheres represent Weyl nodes that act as sources (+) and drains (−), respectively, of the Berry curvature (green arrows)12.

### Extended Data Fig. 6 Experimental conditions for electrical measurements.

a, Sequence used for the SOT-induced switching measurements. b, Thickness dependence of the resistivity of the NM (Pt or W) layer obtained in the Si/SiO2/Ru(2)/Mn3Sn(40)/Pt or W(dNM)/AlOx(5) Hall bar devices at room temperature.

### Extended Data Fig. 7 Current-induced switching, signal stability and heating effects in the Mn3Sn devices.

a–c, Hall voltage versus write current density for Mn3Sn without an NM layer (a), Mn3Sn/Cu (b) and Mn3Sn/Pt (c) Hall bar devices under a bias field of Hx = 0.1 T. In contrast to the Mn3Sn/Pt device (c), which shows clear switching, the Hall voltage of the Mn3Sn sample in a is not switched by the electric current, similarly to the Mn3Sn/Cu sample in b. The top and bottom horizontal axes present the write current Iwrite in whole multilayers and the write current density Jwrite in the Mn3Sn layer, respectively. d, Dependence of the Hall voltage VH on the wait time (twait) measured after electrical switching of the AHE by the write current Iwrite (±50 mA, 100 ms) in the Mn3Sn/Pt(7.2) device at room temperature. No variation of the AHE signal is observed for twait = 600 ms ≈ 1 h, which indicates that 600 ms is long enough to cool the sample down to room temperature, and the AHE signal is very stable in the Mn3Sn Hall bar devices after the electrical switching. e, Hall voltage as a function of the number of write current pulses in the Mn3Sn/Pt(7.2) device at room temperature. The AHE signal obtained after the first write current (±50 mA, 100 ms) does not change even after five consecutive pulses, similarly to FMs29.

### Extended Data Fig. 8 Crystal grain configurations in the polycrystalline Mn3Sn layer.

ac, Configurations of the SOT-induced switching in the Si/SiO2/Ru(2)/Mn3Sn(40)/Pt and W (dNM)/AlOx(5) Hall bar devices. a, Configuration (b): the kagome layer is parallel to I and perpendicular to p. b, Configuration (c): the kagome layeris parallel to the current I and parallel to the electrically injected carrier spin polarization p. Green arrows represent the spin polarized current in the NM (for example, Pt) induced by the write current along the x direction. The crystal and magnetic structures of Mn3Sn are presented (Fig. 1a, b). c, In-plane angle φ (as defined in Fig. 4c) of the octupole moment as a function of time t for the configuration (b). The coordinates x, y and z are defined as in a. The damping-like torque is applied at t > 21.5 ns. Inset, magnified view of the in-plane angle φ of the octupole moment as a function of time. The results indicate continuous rotation of a slightly canted ITS structure with a frequency of ~3.5 THz.

### Extended Data Fig. 9 Kagome plane arrangements for configuration (a).

a, b, Kagome plane orientations (a-1) b axis $$[01\bar{1}0]$$ parallel to y (a); (a-2) a axis $$[2\bar{1}\bar{1}0]$$ parallel to ywhere the kagome layer is normal to the current I and parallel to y. The broken arrows represent the magnetic easy axis of the octupole polarization.

### Extended Data Fig. 10 Simulated dynamics of the sublattice moments during the switching.

a, In-plane motions of the octupole polarization in the absence of a bias field. The red (blue) line corresponds to the motion under Iwrite > 0 (Iwrite < 0). Here, we use a write current with a finite rise time to suppress the incoherent oscillating behaviour. The inset shows a magnified view of the short period right after the current injection at t1. The parameters used here are the same as those used in Fig. 4b. b, Evolution of the out-of-(kagome)plane components (parallel to the x direction) of the sublattice magnetic moments m1 (red), m2 (blue) and m3 (green), induced by Iwrite < 0. θma > 0 (θma < 0) (a = 1, 2, 3) corresponds to the positive (negative) component in the x direction from the yz (kagome) plane.

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Tsai, H., Higo, T., Kondou, K. et al. Electrical manipulation of a topological antiferromagnetic state. Nature 580, 608–613 (2020). https://doi.org/10.1038/s41586-020-2211-2

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