  Applying a temperature gradient in a magnetic material generates a voltage
that is perpendicular to both the heat flow and the magnetization. This is the
anomalous Nernst effect (ANE) which was thought to be proportional to the value
of the magnetization for a long time. However, more generally, the ANE has been
predicted to originate from a net Berry curvature of all bands near the Fermi
level. Subsequently, a large anomalous Nernst thermopower has recently been
observed in topological materials with no net magnetization but large net Berry
curvature around E$_F$. These experiments clearly fall outside the scope of the
conventional magnetization-model of the ANE, but a significant question
remains: Can the value of the ANE in topological ferromagnets exceed the
highest values observed in conventional ferromagnets? Here, we report a
remarkably high anomalous Nernst thermopower value of ~6.0 \mu V/K at 1 T in
the ferromagnetic topological Heusler compound Co$_2$MnGa at room temperature,
which is around 7-times larger than any anomalous Nernst thermopower value ever
reported for a conventional ferromagnet. Combined electrical, thermoelectric
and first-principles calculations reveal that this high value of the ANE arises
from a large net Berry curvature near the Fermi level associated with nodal
lines and Weyl points.
