  The chirality, i.e. left or right handedness, is an important notion in a
broad range of science. In condensed matter, this occurs not only in molecular
or crystal forms but also in magnetic structures. A magnetic skyrmion, a
topologically-stable spin vortex structure, as observed in chiral-lattice
helimagnets is one such example; the spin swirling direction (skyrmion
helicity) should be closely related to the underlying lattice chirality via the
relativistic spin-orbit coupling (SOC). Here, we report on the correlation
between skyrmion helicity and crystal chirality as observed by Lorentz
transmission electron microscopy (TEM) and convergent-beam electron diffraction
(CBED) on the composition-spread alloys of helimagnets Mn1-xFexGe over a broad
range (x = 0.3 - 1.0) of the composition. The skyrmion lattice constant or the
skyrmion size shows non-monotonous variation with the composition x,
accompanying a divergent behavior around x = 0.8, where the correlation between
magnetic helicity and crystal chirality is reversed. The underlying mechanism
is a continuous x-variation of the SOC strength accompanying sign reversal in
the metallic alloys. This may offer a promising way to tune the skyrmion size
and helicity.
