  Many questions are still open regarding the physical mechanisms behind the
magnetic switching in GdFeCo alloys by single optical pulses. Phenomenological
models suggest a femtosecond scale exchange relaxation between sublattice
magnetization as the driving mechanism for switching. The recent observation of
thermally induced switching in GdFeCo by using both several picosecond optical
laser pulse as well as electric current pulses has questioned this previous
understanding. This has raised the question of whether or not the same
switching mechanics are acting at the femo- and picosecond scales. In this
work, we aim at filling this gap in the understanding of the switching
mechanisms behind thermal single-pulse switching. To that end, we have studied
experimentally thermal single-pulse switching in GdFeCo alloys, for a wide
range of system parameters, such as composition, laser power and pulse
duration. We provide a quantitative description of the switching dynamics using
atomistic spin dynamics methods with excellent agreement between the model and
our experiments across a wide range of parameters and timescales, ranging from
femtoseconds to picoseconds. Furthermore, we find distinct element-specific
damping parameters as a key ingredient for switching with long picosecond
pulses and argue, that switching with pulse durations as long as 15 picoseconds
is possible due to a low damping constant of Gd. Our findings can be easily
extended to speed up dynamics in other contexts where ferrimagnetic GdFeCo
alloys have been already demonstrated to show fast and energy-efficient
processes, e.g. domain-wall motion in a track and spin-orbit torque switching
in spintronics devices.
