  Energy loss due to ohmic heating is a major bottleneck limiting down-scaling
and speed of nano-electronic devices, and harvesting ohmic heat for signal
processing is a major challenge in modern electronics. Here we demonstrate that
thermal gradients arising from ohmic heating can be utilized for excitation of
coherent auto-oscillations of magnetization and for generation of tunable
microwave signals. The heat-driven dynamics is observed in
$\mathrm{Y_{3}Fe_{5}O_{12}/Pt}$ bilayer nanowires where ohmic heating of the Pt
layer results in injection of pure spin current into the
$\mathrm{Y_{3}Fe_{5}O_{12}}$ layer. This leads to excitation of
auto-oscillations of the $\mathrm{Y_{3}Fe_{5}O_{12}}$ magnetization and
generation of coherent microwave radiation. Our work paves the way towards spin
caloritronic devices for microwave and magnonic applications.
