We probe the current-induced magnetic switching of insulating antiferromagnet/heavy metals systems, by electrical spin Hall magnetoresistance measurements and direct imaging, identifying a reversal occurring by domain wall (DW) motion. We observe switching of more than one third of the antiferromagnetic domains by the application of current pulses. Our data reveal two different magnetic switching mechanisms leading together to an efficient switching, namely the spin-current induced effective magnetic anisotropy variation and the action of the spin torque on the DWs. 2 MANUSCRIPTElectrical read-out and writing of the antiferromagnetic state is crucial to exploit the properties of antiferromagnets in future spintronic devices. Antiferromagnetic materials have the potential for ultrafast operation [1], with spin dynamics in the terahertz range, high packing density, due to the absence of stray magnetic fields, and an insensitivity to magnetic fields [2,3]. Furthermore, low-power operation is possible in antiferromagnetic insulators (AFM-Is) due to long spin diffusion lengths [4] and the theoretical prediction of superfluid spin transport [5].Recently, the electrical reading of the Néel order (n) orientation in AFM-Is was demonstrated via spin Hall magnetoresistance (SMR) [6-10], a magnetoresistive effect depending on the mutual orientation of the magnetic order and an interfacial spin accumulation μs. However, one of the main challenges faced by AFM spintronics is the reliable electrical writing of the orientation of n. One possible approach exploits staggered Néel spin orbit torques [11], creating an effective field of opposite sign on each magnetic sublattice. However, these torques rely on special material requirements, which has limited their application to the conducting AFMs CuMnAs and Mn2Au [12][13][14][15][16]. Another approach would be to use the non-staggered, antidamping-like torque exerted by a spin accumulation at the interface of a heavy metal and an AFM-I. A charge current in the heavy metal layer can generate a transverse spin current via the spin Hall effect, creating antidamping-like torques in the antiferromagnet.The possibility of such switching was demonstrated in NiO(001)/Pt and Pt/NiO(111)/Pt [17,18], but the mechanisms are still debated. One of the possible mechanisms relies on spin-current induced domain wall (DW) motion [19], predicting that DWs with opposite chirality are driven in opposite directions, thus excluding the electrical signature of the switching when DWs with opposite chirality are equally probable. A second mechanism [18], based on the coherent rotation of n, predicts a current threshold ten times larger than that found experimentally. A third mechanism, based on field-like torques acting on uncompensated interfacial spins, requires perfectly flat interfaces [17]. Currently, none of these provides a consistent explanation of the effect.In this work we realize reliable current-induced switching in epitaxial antiferromagnetic NiO/Pt bilayers. We show that the magnetic state of ...

We report the observation of the three-dimensional angular dependence of the spin Hall magnetoresistance (SMR) in a bilayer of the epitaxial antiferromagnetic insulator NiO(001) and the heavy metal Pt, without any ferromagnetic element. The detected angular-dependent longitudinal and transverse magnetoresistances are measured by rotating the sample in magnetic fields up to 11 T, along three orthogonal planes (xy-, yz-and xz-rotation planes, where the z-axis is orthogonal to the sample plane). The total magnetoresistance has contributions arising from both the SMR and ordinary magnetoresistance. The onset of the SMR signal occurs between 1 and 3 T and no saturation is visible up to 11 T. The three-dimensional angular dependence of the SMR can be explained by a model considering the reversible field-induced redistribution of magnetostrictive antiferromagnetic S-and T-domains in the NiO(001), stemming from the competition between the Zeeman energy and the elastic clamping effect of the non-magnetic MgO substrate. From the observed SMR ratio, we estimate the spin mixing conductance at the NiO/Pt interface to be greater than 2x10 14 Ω -1 m -2 . Our results demonstrate

In the field of antiferromagnetic (AFM) spintronics, information about the Néel vector, AFM domain sizes, and spin-flop fields is a prerequisite for device applications but is not available easily. We have investigated AFM domains and spin-flop induced changes of domain patterns in Mn 2 Au(001) epitaxial thin films by X-ray magnetic linear dichroism photoemission electron microscopy (XMLD-PEEM) using magnetic fields up to 70 T. As-prepared Mn 2 Au films exhibit AFM domains with an average size ≤1 µm. Application of a 30 T field, exceeding the spin-flop field, along a magnetocrystalline easy axis dramatically increases the AFM domain size with Néel vectors perpendicular to the applied field direction. The width of Néel type domain walls (DW) is below the spatial resolution of the PEEM and therefore can only be estimated from an analysis of the DW profile to be smaller than 80 nm. Furthermore, using the values for the DW width and the spin-flop field, we evaluate an in-plane anisotropy constant ranging between 1 and 17 µeV/f.u.. arXiv:1803.03022v1 [cond-mat.mtrl-sci]