Nucleation and annihilation of skyrmions in Mn 2 CoAl observed through the topological Hall effect.

Magnetic skyrmions are topologically protected spin textures with great technological potential. These topologically non-trivial non-coplanar spin textures give rise to a topological Hall effect, enabling the purely electronic detection of magnetic skyrmions. We report a clear topological Hall effect in thin films of the the Heusler alloy Mn2 CoAl, a ferromagnetic spin-gapless semiconductor, capped by a thin layer of Pd. We exploit the strong thickness- and temperature-dependence of the anomalous Hall effect in this system, tuning it to zero to enable the unambiguous measurement of the topological Hall effect, which is observed for temperatures between 3 K and 280 K. The topological Hall effect is evidence of skyrmions, and we demonstrate the simultaneous coexistence of opposite polarity skyrmions using a novel method involving minor field loops of the Hall effect.