Vortex propagation and phase transitions in a chiral antiferromagnetic nanostripe

We study a vortex in a nanostripe of an antiferromagnet with easy-plane anisotropy and interfacial Dzyaloshinskii-Moriya interaction. The vortex has hybrid chirality, being of Neel type close to its center and of Bloch type away from it. Propagating vortices can acquire velocities up to a maximum value that is lower than the spin wave velocity. Theoretical arguments lead to the general result that the velocity of localized excitations in chiral antiferromagnets cannot reach the spin wave velocity. When the vortex is forced to exceed the maximum velocity, phase transitions occur to a nonflat spiral, vortex chain, and flat spiral, successively. The vortex chain is a topological configuration stabilized in the stripe geometry.