Anomalous Nernst and Seebeck Effects in NiCo2O4 Films

Abstract

We investigated both the Seebeck and anomalous Nernst e ff ects in NiCo 2 O 4 (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 e ffi ciency of NiCo 2 O 4 is quite small compared to conventional ferromagnetic metals.