  We present a microscopic magnetic domain imaging study of single-shot
all-optical magnetic toggle switching of a ferrimagnetic Gd$_{26}$Fe$_{74}$
film with out-of-plane easy axis of magnetization by x-ray magnetic circular
dichroism photoelectron emission microscopy. Individual linearly polarized
laser pulses of 800 nm wavelength and 100 fs duration above a certain threshold
fluence reverse the sample magnetization, independent of the magnetization
direction, the so-called toggle switching. Local deviations from this
deterministic behavior close to magnetic domain walls are studied in detail.
Reasons for nondeterministic toggle switching are related to extrinsic effects,
caused by pulse-to-pulse variations of the exciting laser system, and to
intrinsic effects related to the magnetic domain structure of the sample. The
latter are, on the one hand, caused by magnetic domain wall elasticity, which
leads to a reduction of the domain-wall length at sharp tipped features. These
features appear after the optical switching at positions where the line of
constant threshold fluence in the Gaussian footprint of the laser pulse comes
close to an already-existing domain wall. On the other hand, we identify the
presence of laser-induced domain-wall motion in the toggle-switching event as a
further cause for local deviations from purely deterministic toggle switching.
