In metallic ferromagnets, the Berry curvature of underlying quasiparticles can cause an electric voltage perpendicular to both magnetization and an applied temperature gradient, a phenomenon called the anomalous Nernst effect (ANE) [1,2]. Here, we report the observation of a giant ANE in the full-Heusler ferromagnet Co 2 MnGa, reaching S yx ∼ −6 µV/K at room T , one order of magnitude larger than the maximum value reported for a magnetic conductor [3]. With increasing temperature, the transverse thermoelectric conductivity or Peltier coefficient α yx shows a crossover between T -linear and −T log(T ) behaviors, indicating the violation of Mott formula at high temperatures. Our numerical and analytical calculations indicate that the proximity to a quantum Lifshitz transition between type-I and type-II magnetic Weyl fermions [4-6] is responsible for the observed crossover properties and an enhanced α yx . The

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Crystal structure and magnetic properties of Heusler-alloy Co2MnGa were examined systematically using non-stoichiometric compositions of Co and Mn element from the Czochralski as-grown single crystal samples. The crystalline structure of each sample was characterized by means of X-ray powder diffraction technique. Each sample was treated with and without heat treatment at 923 K for 10 hours. The effects of Co and Mn excess were observed in the lattice constants for both treatments. The L21-type crystal structure was observed only for the heat-treated samples. The changes in lattice constants are attributed to the substitution of atomic sites. The excess of Co tends to decrease the crystal volume, in opposite to the excess of Mn. In order to investigate the Slater-Pauling rule in the non-stoichiometric samples, the saturation magnetic moments were measured from the field-dependent magnetization measurement for the as-grown samples at 2 K. The deviation from the Slater-Pauling rule was found in the lower concentration of valence electron which associated to the lower total fraction of both Co and Mn. This indicates that the magnetic interactions of these materials cannot only be contributed to the number of valence electron.