  In the quest for post-CMOS technologies, ferromagnetic skyrmions and their
anti-particles have shown great promise as topologically protected solitonic
information carriers in memory-in-logic or neuromorphic devices. However, the
presence of dipolar fields in ferromagnets, restricting the formation of
ultra-small topological textures, and the deleterious skyrmion Hall effect when
driven by spin torques have thus far inhibited their practical implementations.
Antiferromagnetic analogues, which are predicted to demonstrate relativistic
dynamics, fast deflection-free motion and size scaling have recently come into
intense focus, but their experimental realizations in natural antiferromagnetic
systems are yet to emerge. Here, we demonstrate a family of topological
antiferromagnetic spin-textures in $\alpha$-Fe$_2$O$_3$ - an earth-abundant
oxide insulator - capped with a Pt over-layer. By exploiting a first-order
analogue of the Kibble-Zurek mechanism, we stabilize exotic merons-antimerons
(half-skyrmions), and bimerons, which can be erased by magnetic fields and
re-generated by temperature cycling. These structures have characteristic sizes
of the order ~100 nm that can be chemically controlled via precise tuning of
the exchange and anisotropy, with pathways to further scaling. Driven by
current-based spin torques from the heavy-metal over-layer, some of these AFM
textures could emerge as prime candidates for low-energy antiferromagnetic
spintronics at room temperature.
