† 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...

Large spin splitting at Rashba interface, giving rise to strong spin-momentum locking, is essential for efficient spin-to-charge conversion. Recently, a Cu/Bismuth oxide (Bi2O3) interface has been found to exhibit an efficient spin-to-charge conversion similar to a Ag/Bi interface with large Rashba spin splitting. However, the guiding principle of designing the metal/oxide interface for the efficient conversion has not been clarified yet. Here we report strong non-magnetic (NM) material dependence of spin splitting at NM/Bi2O3 interfaces. We employed spin pumping technique to inject spin current into the interface and evaluated the magnitude of interfacial spin-to-charge conversion. We observed large modulation and sign change in conversion coefficient which corresponds to the variation of spin splitting. Our experimental results together with first-principles calculations indicate that such large variation is caused by material dependent electron distribution near the interface. The results suggest that control of interfacial electron distribution by tuning the difference in work function across the interface may be an effective way to tune the magnitude and sign of spin-to-charge conversion and Rashba parameter at interface.

We report the direct observation of uniform in-plane spin accumulation at room temperature by magneto optical Kerr effect, at the interface formed between nonmagnetic metal (Cu, Ag) and oxide (Bi2O3). Recent reports show spin to charge conversion at these interfaces suggesting the presence of Rashba like spin orbit coupling (SOC). The formation of spin accumulation is the result of current induced spin polarization at our interfaces (direct Rashba–Edelstein effect), without external magnetic field or proximity to ferromagnetic materials. We observe opposite orientation of spin accumulation at Cu/Bi2O3 and Ag/Bi2O3 interfaces reflecting their opposite sign of Rashba SOC (Rashba parameter). Moreover, estimation of spin accumulation from values of Rashba parameters obtained by independent spin pumping measurements, agrees well with the difference in amplitude of our normalized Kerr signals for Cu/Bi2O3 and Ag/Bi2O3 interfaces. Uniform in-plane spin accumulation due to Rashba-Edelstein effect can be applied for spin filter devices and efficient driving force for magnetization switching.

The tunnelling electric current passing through a magnetic tunnel junction (MTJ) is strongly dependent on the relative orientation of magnetizations in ferromagnetic electrodes sandwiching an insulating barrier, rendering efficient readout of spintronics devices1–5. Thus, tunnelling magnetoresistance (TMR) is considered to be proportional to spin polarization at the interface1 and, to date, has been studied primarily in ferromagnets. Here we report observation of TMR in an all-antiferromagnetic tunnel junction consisting of Mn3Sn/MgO/Mn3Sn (ref. 6). We measured a TMR ratio of around 2% at room temperature, which arises between the parallel and antiparallel configurations of the cluster magnetic octupoles in the chiral antiferromagnetic state. Moreover, we carried out measurements using a Fe/MgO/Mn3Sn MTJ and show that the sign and direction of anisotropic longitudinal spin-polarized current in the antiferromagnet7 can be controlled by octupole direction. Strikingly, the TMR ratio (about 2%) of the all-antiferromagnetic MTJ is much larger than that estimated using the observed spin polarization. Theoretically, we found that the chiral antiferromagnetic MTJ may produce a substantially large TMR ratio as a result of the time-reversal, symmetry-breaking polarization characteristic of cluster magnetic octupoles. Our work lays the foundation for the development of ultrafast and efficient spintronic devices using antiferromagnets8–10.