  We adapt the non-linear $\sigma$ model to study the nonequilibrium critical
dynamics of O(n) symmetric ferromagnetic system. Using the renormalization
group analysis in $d=2+\epsilon$ dimensions we investigate the pure relaxation
of the system starting from a completely ordered state. We find that the
average magnetization obeys the long-time scaling behavior almost immediately
after the system starts to evolve while the correlation and response functions
demonstrate scaling behavior which is typical for aging phenomena. The
corresponding fluctuation-dissipation ratio is computed to first order in
$\epsilon$ and the relation between transverse and longitudinal fluctuations is
discussed.
