Large anomalous Nernst and inverse spin-Hall effects in epitaxial thin films of kagome semimetal Mn3Ge

Synthesis of crystallographically well-defined thin films of topological materials is important for unraveling their mesoscale quantum properties and for device applications. ${\mathrm{Mn}}_{3}\mathrm{Ge}$, an antiferromagnetic Weyl semimetal with a chiral magnetic structure on a kagome lattice, is expected to have enhanced Berry curvature around Weyl nodes near the Fermi energy, leading to large anomalous Hall/Nernst effects and a large spin-Hall effect. Using magnetron sputtering, we have grown epitaxial thin films of hexagonal $\mathrm{D}{0}_{19}\phantom{\rule{4pt}{0ex}}{\mathrm{Mn}}_{3}\mathrm{Ge}$ that are flat and continuous. Large anomalous Nernst and inverse spin-Hall effects are observed in thermoelectric and spin-pumping devices. The anomalous Nernst signal in our ${\mathrm{Mn}}_{3}\mathrm{Ge}$ films is estimated to be 0.1 \ensuremath{\mu}V/K and is comparable to that in ferromagnetic Fe, despite ${\mathrm{Mn}}_{3}\mathrm{Ge}$ having a weak magnetization of $\ensuremath{\sim}3.5\phantom{\rule{0.16em}{0ex}}\mathrm{m}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Mn}$ at room temperature. The spin-mixing conductance is $90.5\phantom{\rule{0.16em}{0ex}}{\mathrm{nm}}^{\ensuremath{-}2}$ at the $\mathrm{Py}/{\mathrm{Mn}}_{3}\mathrm{Ge}$ interface, and the spin-Hall angle in ${\mathrm{Mn}}_{3}\mathrm{Ge}$ is estimated to be about eight times of that in Pt.