Anomalous Nernst and Seebeck Effects in NiCo₂O₄ Films

Abstract

  We investigated both the Seebeck and anomalous Nernst effects in NiCo₂O₄(001) epitaxial films with a preferential magnetization direction normal to the film plane. Since the thermoelectric signals were extremely small, we custom-built a measurement system to detect the weak voltage signals. To suppress spurious voltage signals originating from the electrical contacts in the measurement circuit, we employed the following measures. We reduced the number of electrical contacts between the output of a commercial cryostat with a superconducting magnet and the nano-voltmeters. We employed silver soldering while making the electrical contacts to reduce the thermal electromotive force voltages at the remaining contacts. By adopting these measures, we have succeeded in detecting thermoelectric voltages as small as 5 nV. The observed thermoelectric efficiency of NiCo₂O₄ is quite small compared to conventional ferromagnetic metals.