We study a spin Hamiltonian for spin-orbit-coupled ferromagnets on the honeycomb lattice. At sufficiently low temperatures supporting the ordered phase, the effective Hamiltonian for magnons, the quanta of spin-wave excitations, is shown to be equivalent to the Haldane model for electrons, which indicates the nontrivial topology of the band and the existence of the associated edge state. At high temperatures comparable to the ferromagnetic-exchange strength, we take the Schwingerboson representation of spins, in which the mean-field spinon band forms a bosonic counterpart of the Kane-Mele model. The nontrivial geometry of the spinon band can be inferred by detecting the spin Nernst effect. A feasible experimental realization of the spin Hamiltonian is proposed. Introduction.-Electronic systems with spin-orbit coupling (SOC) can exhibit spin Hall effects, in which a longitudinal electric field generates a transverse spin current and vice versa [1]. In particular, Kane and Mele [2] showed that a single layer of graphene has a topologically nontrivial band structure with an SOC-induced energy gap, which gives rise to a quantum spin Hall effect characterized by helical edge states. This identification of graphene as a quantum spin Hall insulator has served as a starting point for the search for other topological insulators [3,4].

We investigate the current-induced switching of the Néel order in NiO(001)/Pt heterostructures, which is manifested electrically via the spin Hall magnetoresistance. Significant reversible changes in the longitudinal and transverse resistances are found at room temperature for a current threshold lying in the range of 10^{7}  A/cm^{2}. The order-parameter switching is ascribed to the antiferromagnetic dynamics triggered by the (current-induced) antidamping torque, which orients the Néel order towards the direction of the writing current. This is in stark contrast to the case of antiferromagnets such as Mn_{2}Au and CuMnAs, where fieldlike torques induced by the Edelstein effect drive the Néel switching, therefore resulting in an orthogonal alignment between the Néel order and the writing current. Our findings can be readily generalized to other biaxial antiferromagnets, providing broad opportunities for all-electrical writing and readout in antiferromagnetic spintronics.

Spin superfluidity, i.e., coherent spin transport mediated by topologically stable textures, is limited by parasitic anisotropies rooted in relativistic interactions and spatial inhomogeneities. Since structural disorder in amorphous magnets can average out the effect of these undesired couplings, we propose this class of materials as platforms for superfluid spin transport. We establish nonlinear equations describing the hydrodynamics of spin in insulating amorphous magnets, where the currents are defined in terms of coherent rotations of a noncollinear texture. Our theory includes dissipation and nonequilibrium torques at the interface with metallic reservoirs. This framework allows us to determine different regimes of coherent dynamics and their salient features in nonlocal magneto-transport measurements. Our work paves the way for future studies on macroscopic spin dynamics in materials with frustrated interactions. arXiv:1803.01309v2 [cond-mat.mes-hall]

We analyze the dynamics of electrons in corrugated layers of transition metal dichalcogenides. The intrinsic (Gaussian) curvature along with the strong spin-orbit interaction leads to an emergent gauge field associated with the Berry connection of the spinor wave function. We study in detail the effect of topological defects of the lattice, namely tetragonal/octogonal disclinations and edge dislocations. Ripples and topological disorder induce the same dephasing effects as a random magnetic field, suppressing the weak localization effects. This geometric magnetic field can be detected in a Aharonov-Bohm interferometry experiment by measuring the local density of states in the vicinity of corrugations.

We study the emergence and dynamics of in-plane skyrmions in collinear ferromagnetic heterostructures. We present a minimal energy model for this class of magnetic textures, determine the crystal symmetries compatible with it and propose material candidates, based on symmetries only, for the observation of these topological solitons. We calculate exact solutions of the energy model for in-plane skyrmions in the absence of dipolar interactions at critical coupling, the latter defined by the relations H = K and D = √ AK for the strength of the external magnetic field and the Dzyaloshinskii coupling constant, respectively, with K and A being the anisotropy constant and the exchange stiffness of the material. Through micromagnetic simulations, we demonstrate the possibility of in-plane skyrmion production via i) the motion of domain walls through a geometrical constriction and ii) shedding from a magnetic impurity driven both by spin transfer torques. In-plane skyrmion dynamics triggered by spin-orbit torques are also investigated analytically and numerically. Our findings point towards the possibility of designing racetracks for in-plane skyrmions, whose speed could be tuned by adjusting the angle between the charge current and the uniform background magnetization; in particular, the speed is maximum for currents parallel to the easy axis and becomes zero for currents transverse to it. arXiv:1910.00987v2 [cond-mat.mes-hall]