  Outstanding crystalline perfection is a key requirement for the formation of
new forms of electronic order in a vast number of widely different materials.
Whereas excellent sample quality represents a standard claim in the literature,
there are, quite generally, no reliable microscopic probes to establish the
nature and concentration of lattice defects such as voids, dislocations and
different species of point defects on the level relevant to the length and
energy scales inherent to these new forms of order. Here we report an
experimental study of the archetypical skyrmion-lattice compound MnSi, where we
relate the characteristic types of point defects and their concentration to the
magnetic properties by combining different types of positron spectroscopy with
ab-initio calculations and bulk measurements. We find that Mn antisite disorder
broadens the magnetic phase transitions and lowers their critical temperatures,
whereas the skyrmion lattice phase forms for all samples studied underlining
the robustness of this topologically non-trivial state. Taken together, this
demonstrates the unprecedented sensitivity of positron spectroscopy in studies
of new forms of electronic order.
