  By employing magnetization and small angle neutron scattering (SANS)
measurements, we have investigated the behavior of the skyrmion lattice (SKL)
and the helical order in MnSi0.992Ga0.008. Our results indicate that the order
of the SKL is sensitive to the orientation of an applied magnetic field with
respect to the crystal lattice and small variations in the sequence of
temperature and applied magnetic field changes. The disorder caused by the
substitution of the heavier element Ga for Si is sufficient to reduce the
pinning of the SKL to the underlying crystalline lattice. This reduces the
propensity for the SKL to be aligned with the crystal lattice. This tendency is
most evident when the applied field is not well oriented with respect to the
high symmetry axes of the crystal resulting in disorder in the long range SKL
while maintaining sharp radial order. We have also investigated the effect of
substituting heavier elements into MnSi on the reorientation process of the
helical domains with field cycling in MnSi0.992Ga0.008 and Mn0.985Ir0.015Si. A
comparison of the reorientation process in these materials with field reduction
indicates that the substitution of heavier elements on either Mn or Si sites
creates a higher energy barrier for the reorientation of the helical order and
for the formation of domains.
