  In ferromagnetic solids, even in absence of magnetic field, a transverse
voltage can be generated by a longitudinal temperature gradient. This
thermoelectric counterpart of the Anomalous Hall effect (AHE) is dubbed the
Anomalous Nernst effect (ANE). Expected to scale with spontaneous
magnetization, both these effects arise because of the Berry curvature at the
Fermi energy. Here, we report the observation of a giant ANE in a
newly-discovered magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ crystal. Hall
resistivity and Nernst signal both show sharp jumps at a threshold field and
exhibit a clear hysteresis loop below the ferromagnetic transition temperature.
The ANE signal peaks a maximum value of about 5 miuV/K which is comparable to
the largest seen in any magnetic material. Moreover, the anomalous transverse
thermoelectric conductivity becomes as large as about 10 A/K.m at 70 K, the
largest in known semimetals. The observed ANE signal is much larger than what
is expected according to the magnetization.
