Effect of sample size on anomalous Nernst effect in chiral antiferromagnetic Mn₃Sn devices

We investigate the effect of sample size on the anomalous Nernst effect (ANE) in a device formed from chiral antiferromagnetic Mn₃Sn. We also investigate its magnetic domains by employing focused ion beam lithography. Mn₃Sn is a suitable material for studying the thermoelectric effect in the presence of antiferromagnetic domains because it exhibits a large ANE. In the Mn₃Sn device used in this study, a Ta layer acts as a heater; the heat produced via Joule heating diffuses through a sapphire substrate into the thin flake of Mn₃Sn. The Nernst signal exhibits a stepwise hysteresis when the sample is subjected to a temperature gradient and magnetic field at 290 K. The stepwise hysteresis depends on the sample shape and size—which affect nucleation, pinning, and depinning processes—but the temperature difference also has a significant effect on the switching process. The domain ratios calculated using the ANE results indicate that the domain size is smaller than 20 μm². This obtained domain size is in good agreement with the reported experimental values of 10–100 μm² for the magneto-optical Kerr effect in bulk single-crystal Mn₃Sn. Thus, the ANE is a powerful means of obtaining information about the magnetic domains in samples under a temperature gradient, thereby promising a reliable approach to study magnetic domains and spintronics using antiferromagnets.