  Time-resolved pump-probe measurements were made at variable heat accumulation
in Co/Pd superlattices. Heat accumulation increases the baseline temperature
and decreases the equilibrium magnetization. Transient ultrafast
demagnetization first develops with higher fluence in parallel with strong
equilibrium thermal spin fluctuations. The ultrafast demagnetization is then
gradually removed as the equilibrium temperature approaches the Curie
temperature. The transient magnetization time-dependence is fit well with the
spin-flip scattering model.
