  Magnetization manipulation in the absence of an external magnetic field is a
topic of great interest, since many novel physical phenomena need to be
understood and promising new applications can be imagined. Cutting-edge
experiments have shown the capability to switch the magnetization of magnetic
thin films using ultrashort polarized laser pulses. In 2007, it was first
observed that the magnetization switching for GdFeCo alloy thin films was
helicity-dependent and later helicity-independent switching was also
demonstrated on the same material. Recently, all-optical switching has also
been discovered for a much larger variety of magnetic materials (ferrimagnetic,
ferromagnetic films and granular nanostructures), where the theoretical models
explaining the switching in GdFeCo films do not appear to apply, thus
questioning the uniqueness of the microscopic origin of all-optical switching.
Here, we show that two different all-optical switching mechanisms can be
distinguished; a "single pulse" switching and a "cumulative" switching process
whose rich microscopic origin is discussed. We demonstrate that the latter is a
two-step mechanism; a heat-driven demagnetization followed by a
helicity-dependent remagnetization. This is achieved by an all-electrical and
time-dependent investigation of the all-optical switching in ferrimagnetic and
ferromagnetic Hall crosses via the anomalous Hall effect, enabling to probe the
all-optical switching on different timescales.
