Rare earth size dependence of Nernst thermopower in ferromagnetic perovskites: R0.6Sr0.4CoO3 (R = La, Pr, and Nd)

Abstract

Here, we report the Nernst thermopower (Sxy)- generation of a dc electrical voltage transverse to the applied temperature gradient and magnetic field- in the ferromagnetic metallic oxide series: R0.6Sr0.4CoO3 for rare earth cations (R = La, Pr and Nd) of different ionic radii. Besides Sxy, longitudinal thermopower (Sxx) and resistivity in absence of an external magnetic field were also measured. In each of these samples, Sxy increases rapidly around the ferromagnetic Curie temperature (TC), goes through a maximum value at a certain temperature, and decreases towards zero in low temperatures. The field dependence of Sxy measured at a fixed temperature exhibits hysteresis similar to magnetization, which indicates magnetic contribution (anomalous) to the measured Sxy. The sample possessing the largest ionic radius (R = La) shows the maximum Sxy value (~0.264 μV/K for H = 2 kOe) in this series. Our work guides that future studies need to be focused on the La-based cobaltites to enhance Sxy value through optimizing compositions.