  Thermal vorticity in non-central Au+Au collisions at energies $7.7 \leq
\sqrt{s} \leq 62.4$ GeV is calculated within the UrQMD transport model. Tracing
the $\Lambda$ and $\bar{\Lambda}$ hyperons back to their last interaction point
we were able to obtain the temperature and the chemical potentials at the time
of emission by fitting the extracted bulk characteristics of hot and dense
medium to statistical model of ideal hadron gas. Then the polarization of both
hyperons was calculated. The polarization of $\Lambda$ and $\bar{\Lambda}$
increases with decreasing energy of nuclear collisions. The stronger
polarization of $\bar{\Lambda}$ is explained by the different space-time
distributions of $\Lambda$ and $\bar{\Lambda}$ and by different freeze-out
conditions of both hyperons.
