  The study of nanoscale chiral magnetic order in polycrystalline materials
with a strong Dzyaloshinkii-Moriya interaction (DMI) is interesting for the
observation of magnetic phenomena at grain boundaries and interfaces. One such
material is sputter-deposited B20 FeGe on Si, which has been actively
investigated as the basis for low-power, high-density magnetic memory
technology in a scalable material platform. Although conventional Lorentz
electron microscopy provides the requisite spatial resolution to probe chiral
magnetic textures in single-crystal FeGe, probing the magnetism of sputtered
B20 FeGe is more challenging because the sub-micron crystal grains add
confounding contrast. We address the challenge of disentangling magnetic and
grain contrast by applying 4-dimensional Lorentz scanning transmission electron
microscopy using an electron microscope pixel array detector. Supported by
analytical and numerical models, we find that the most important parameter for
imaging magnetic materials with polycrystalline grains is the ability for the
detector to sustain large electron doses, where having a high-dynamic range
detector becomes extremely important. Despite the small grain size in sputtered
B20 FeGe on Si, using this approach we are still able to observe helicity
switching of skyrmions and magnetic helices across two adjacent grains as they
thread through neighboring grains. We reproduce this effect using micromagnetic
simulations by assuming that the grains have distinct orientation and magnetic
chirality and find that magnetic helicity couples to crystal chirality. Our
methodology for imaging magnetic textures is applicable to other thin-film
magnets used for spintronics and memory applications, where an understanding of
how magnetic order is accommodated in polycrystalline materials is important.
