Anomalous Nernst effect in a microfabricated thermoelectric element made of chiral antiferromagnet Mn₃Sn

Toward realizing a thermopile made of the chiral anti-ferromagnet Mn₃Sn, focused ion beam (FIB) lithography was employed to microfabricate a thermoelectric element consisting of a Ta/Al₂O₃/Mn₃Sn layered structure. In this device, the Ta layer acts as a heater producing Joule heat diffusing across the Al₂O₃ insulating layer into the thin Mn₃Sn layer. The measured Nernst signal exhibits a clear hysteresis in an applied temperature gradient and magnetic field at 300 K, and its magnitude is proportional to the square of the electrical current applied to the Ta heater. The spontaneous, zero field voltage signal in the device is of the order of a few μV, which is almost the same order of magnitude as observed in the bulk single-crystal Mn₃Sn under a temperature gradient. The anomalous Nernst coefficient S_ANE of the microfabricated element was determined using a temperature gradient simulated by finite-element modeling. The obtained value of $SANE$ is 0.27 μV/K, which is in good agreement with that of the reported experimental value of S_ANE (0.3 μV/K) for bulk single-crystal Mn₃Sn. This result indicates that FIB microfabrication does not significantly alter the thermoelectric properties of bulk Mn₃Sn. As the chiral antiferromagnet produces almost no stray field, our study opens the avenue for the fabrication of an efficient thermopile by densely packing the microfabricated antiferromagnetic elements.