  Ever since its discovery in 1996, ultrafast demagnetization has ignited
immense research interest due to its scientific rigor and technological
potential. A flurry of recent theoretical and experimental investigations has
proposed direct and indirect excitation processes in separate systems. However,
it still lacks a unified mechanism and remains highly debatable. Here, for the
first time, we demonstrate that instead of either direct or indirect
interaction, simultaneous and controlled excitation of both direct and indirect
mechanisms of demagnetization are possible in a multilayers composed of
repeated Co/Pd bi-layers. Moreover, we were able to modulate demagnetization
time (from ~350 fs to ~750 fs) by fluence and thickness dependent indirect
excitation due to heat current flowing vertically downward from top layers,
which is combined with an altogether different scenario of direct irradiation.
Finally, by regulating the pump wavelength we could effectively control the
contribution of indirect process, which gives a confirmation to our
understanding of the ultrafast demagnetization process.
