We report the anomalous Nernst effect (ANE) in large-grain ceramics, nanogranular ceramics, and nanogranular thin films of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Co}{\mathrm{O}}_3$, measured over the temperature range 5–300 K. The study is complemented with thermopower, resistivity, and magnetic measurements. The temperature-dependent ANE below the Curie temperature $T_{\mathrm{C}}$ (240–250 K) is analyzed with the help of longitudinal resistivity and Seebeck using a previously proposed formula derived by a combination of Onsager reciprocity, the Mott formula, and the relation between transverse and longitudinal resistivity, ${\rho }_{xy}\propto {\rho }_{xx}^n$. We observe a characteristic exponent n ∼ 0.4 in agreement with the universal scaling for the bad-metal-type conduction regime. The nanogranular samples are characterized by higher resistivity, lower saturated magnetization, and a higher coercive field compared to large-grain ceramics. On the other hand, the magnitude of the ANE is independent of grain size. This observation likely insinuates that the characteristic length scale characterizing the ANE in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Co}{\mathrm{O}}_3$ is below the grain size of nanogranular samples ∼40 nm. Therefore, the ANE associated with the bad-metal regime is independent of barriers associated with grain surface, which are responsible for activated resistivity and lowered magnetization due to a magnetically “dead” layer. The observation that the advantage of the higher coercive field of nanogranular samples is not deteriorated by a lower ANE is important for possible applications in zero magnetic field.

• Received 9 November 2020
• Accepted 16 February 2021

DOI:https://doi.org/10.1103/PhysRevMaterials.5.035401