  Measurements of the transverse Hall resistance are widely used to investigate
electron transport, magnetization phenomena, and topological quantum states.
Owing to the difficulty of probing transient changes of the transverse
resistance, the vast majority of Hall effect experiments are carried out in
stationary conditions using either dc or ac currents. Here we present an
approach to perform time-resolved measurements of the transient Hall resistance
during current-pulse injection with sub-nanosecond temporal resolution. We
apply this technique to investigate in real-time the magnetization reversal
caused by spin-orbit torques in ferrimagnetic GdFeCo dots. Single-shot Hall
effect measurements show that the current-induced switching of GdFeCo is widely
distributed in time and characterized by significant activation delays, which
limit the total switching speed despite the high domain-wall velocity typical
of ferrimagnets. Our method applies to a broad range of current-induced
phenomena and can be combined with non-electrical excitations to perform
pump-probe Hall effect measurements.
