  Achieving the compositionally ordered state in a substitutional alloy of two
or more species can often be even critical for improving its functional
properties. To produce a highly ordered alloy, a longtime high-temperature (up
to T=1000 K) treatment of the alloy is typically necessary because of
insufficient vacancy concentration (c_v) and their mobility. However, such
processing affects the morphology and complicates the technology of functional
alloys. We show theoretically that the ordering in the practically important
FePt system (Fe_xPt_1-x with x being close to 0.5) is already achievable at
T=450 K for reasonable times t<10^3 s due to frozen nonequilibrium vacancies.
Our simulation is based on the Dienes equation for relaxation of the long-range
order parameter (S), with taking additionally into account that the ordering
kinetics in the alloy is mediated by vacancies. Importantly, the results of
such simulation are in good agreement with previous experimental data on the
ordering kinetics. We also find that nanosecond laser pulses can be employed to
achieve a sufficient level of c_v=10^-5 for effective low-temperature ordering.
