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

Abstract

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.