Electrical manipulation of a topological antiferromagnetic state

Abstract

† These authors contributed equally to this work. Electrical manipulation of emergent phenomena due to nontrivial band topology is a key to realize next-generation technology using topological protection. A Weyl semimetal is a three-dimensional gapless system that hosts Weyl fermions as low-energy quasiparticles 1-4 . It exhibits various exotic phenomena such as large anomalous Hall effect (AHE) and chiral anomaly, which have robust properties due to the topologically protected Weyl nodes 1-23 . To manipulate such phenomena, the magnetic version of Weyl semimetals would be useful as a magnetic texture may provide a handle for controlling the locations of Weyl nodes in the Brillouin zone. Moreover, given the prospects of antiferromagnetic (AF) spintronics for realizing high-density devices with ultrafast operation 24-26 , it would 2 be ideal if one could electrically manipulate an AF Weyl metal. However, no report has appeared on the electrical manipulation of a Weyl metal. Here we demonstrate the electrical switching of a topological AF state and its detection by AHE at room temperature. In particular, we employ a polycrystalline thin film 27 of the AF Weyl metal Mn3Sn 10,13,15,28 , which exhibits zero-field AHE. Using the bilayer device of Mn3Sn and nonmagnetic metals (NMs), we find that an electrical current density of ~10 10 -10 11 A/m 2 in NMs induces the magnetic switching with a large change in Hall voltage, and besides, the current polarity along a bias field and the sign of the spin Hall angle θSH of NMs [Pt (θSH > 0) 29 , Cu(θSH ~ 0), W (θSH < 0) 30 ] determines the sign of the Hall voltage. Notably, the electrical switching in the antiferromagnet is made using the same protocol as the one used for ferromagnetic metals 31,32 . Our observation may well lead to another leap in science and technology for topological magnetism and AF spintronics 33 . Recent extensive studies in condensed matter physics have led to the discoveries of novel quantum phases with nontrivial topology in the electronic band structure 4,34,35 . One example of such topological systems is a Weyl semimetal 1-4 . Two non-degenerate bands linearly touch at a pair of momentum points, forming gapless Weyl fermions with different chiralities in a timereversal-symmetry (TRS) or inversion-symmetry breaking state. These touching points or Weyl nodes act as topologically protected, unit-strength (anti)monopoles of underlying Berry curvature, and lead to various emergent phenomena such as large AHE, anomalous Nernst effect (ANE), chiral anomaly and optical gyrotropy 1-23 .For developing science and technology utilizing novel topological states, a crucial next step would be to manipulate these emergent phenomena electrically. In a Weyl semimetal, the manipulation can be made by moving the Weyl points around in the Brillouin zone. For this purpose, the TRS breaking or magnetic Weyl semimetals are suitable as their magnetic texture 3 may provide a handle for the manipulation. Besides, antiferromagnets (AFMs) have recently attracted significant atte...

Scaling the electrical current switching of exchange bias in fully epitaxial antiferromagnet/ferromagnet bilayers

“…Another possibility would be a double helical AFM MnP 59 and CrAs 60 , which have 1.3µ B /Mn and 1.7µ B /Cr, respectively, and it is worthy of future research on those AFM switching. We note that the similar order of switching current density has been recently realized in the SOT of noncollinear AFM of MGN(2.43 µ B /Mn) and Mn 3 Sn(3.2 µ B /Mn 61 ) with 1.5 and 5 × 10 6 A/cm 2 , respectively 16,17 . Since STT consumes more energy than SOT in traditional STT and SOT of FM 62 , our results may imply that SOT in such AFMs has a great potential to realize even lower current density switching.…”

“…6(d). On the other hand, resent SOT studies of noncollinear AFM Mn 3 Sn demonstrate the manipulation of AFM moments even at 40 nm thick films 17 . Hence, as illustrated in Fig.…”

Localized spin-orbit polaron in magnetic Weyl semimetal Co3Sn2S2

“…he transition metal based kagome lattice compounds have merged recently as a novel materials platform for unveiling and exploring the rich and unusual physics of geometric frustration, correlation and magnetism, and the topological behaviors of the quantum electronic states [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . These are layered crystalline materials where the transition metal elements occupy the vertices of the two-dimensional network of corner-sharing triangles, supporting electronic band structures with Dirac crossings and nearly flat bands with strong spin-orbit coupling [19][20][21] .…”

“…These are layered crystalline materials where the transition metal elements occupy the vertices of the two-dimensional network of corner-sharing triangles, supporting electronic band structures with Dirac crossings and nearly flat bands with strong spin-orbit coupling [19][20][21] . The prototype materials include Fe 3 Sn 2 [1][2][3] , FeSn 4 , Co 3 Sn 2 S 2 5,6 , CoSn 7 , Mn 3 Sn [8][9][10][11] , and rare earth (Re) ReMn 6 Sn 6 12,15 . They exhibit different magnetic ground states, such as ferromagnetic (Fe 3 Sn 2 , Co 3 Sn 2 S 2 ), antiferromagnetic (FeSn, Mn 3 Sn), and paramagnetic (CoSn), and often anomalous transport properties of underlying topological origins 5,6,16 .…”

Prospect of Spin-Orbitronic Devices and Their Applications

“…( Finley and Liu, 2016 ; Mishra et al., 2017 ; Yu et al., 2019 ; Pham et al., 2018 ; Kim et al., 2017 ; Han et al., 2017 ; An et al., 2018b ; Cai et al., 2020 ) provide alternative approaches toward the AFM spin-orbitronics with advantages in processing speed (much higher precession frequency than FMs), data scalability (no stray field), and information security (zero net magnetization, and insensitive to external magnetic field). To date, the SOT-induced manipulation of skyrmions motion ( Jiang et al., 2015 ; Buttner et al., 2017 ; Yu et al., 2016 ) (the topological spin textures stabilized by Dzyaloshinskii-Moriya interactions, DMI, see Figure 6 B) and magnetization switching in magnetic insulators ( Avci et al., 2017 ; Shao et al., 2018 ), ferromagnetic topological insulators ( Fan et al., 2014b , 2016 ), antiferromagnetic Weyl semimetals ( Tsai et al., 2020 ), and 2D ferromagnets ( Wang et al., 2019a ; Alghamdi et al., 2019 ; Ostwal et al., 2020 ) (see Figure 6 C) have already been studied intensively, and it is believed that extensive investigations of SOTs in other exotic magnetic materials, such as ferromagnetic Weyl semimetals ( Liu et al., 2019b ; Morali et al., 2019 ; Belopolski et al., 2019 ) and antiferromagnetic topological insulator ( Guin et al., 2019 ; Ghosh and Manchon, 2017 ; Otrokov et al., 2019 ) could attract intriguing interests to enrich the understanding of fundamental SOC physics and corresponding potential applications. Note that the giant amplitude of inverse and direct Rashba-Edelstein effect in oxide heterostructures of SrTiO 3 and LaAlO 3 /SrTiO 3 formed quasi 2D electron gas (2DEG) system also provide significant charge-spin interconversions ( Noël et al., 2020 ), holding the promise to pave the way from oxide spin-orbitronics prospect toward low-power electrical control of magnetizations.…”