Motivated by the recent discovery of a large anomalous Nernst effect in ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Ga}$, ${\mathrm{Fe}}_{3}X$ ($X$=Al, Ga) and ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$, we performed a first-principles study to clarify the origin of the enhancement of the transverse thermoelectric conductivity ${\alpha }_{ij}$ in these ferromagnets. The intrinsic contribution to ${\alpha }_{ij}$ can be understood in terms of the Berry curvature $\mathrm{\Omega }$ around the Fermi level, and $\mathrm{\Omega }$ is singularly large along nodal lines (which are gapless in the absence of the spin-orbit coupling) in the Brillouin zone. We find that not only the Weyl points but also stationary points in the energy dispersion of the nodal lines play a crucial role. The stationary points make sharp peaks in the density of states projected onto the nodal line, clearly identifying the characteristic Fermi energies at which ${\alpha }_{ij}$ is most dramatically enhanced. We also find that ${\alpha }_{ij}/T$ breaks the Mott relation and show a peculiar temperature dependence at these energies. The present results suggest that the stationary points will give us a useful guiding principle to design magnets showing a large anomalous Nernst effect.

• Received 14 September 2020
• Revised 2 November 2020
• Accepted 3 November 2020

DOI:https://doi.org/10.1103/PhysRevB.102.205128