  We report a study of the topological Hall effect (THE) in Fe-doped MnSi and
compare with results from pure MnSi under pressure. We find that Fe doping
increases the THE, indicating an enhancement of the magnitude of the emergent
gauge field. This is consistent with the concurrent reduction in the length
scale of the skyrmion lattice. For both pressurized and doped samples, we
calculate the emergent magnetic field based on the size of the measured THE,
and compare it with a theoretical upper-bound. We find that the ratio of these
two remains more or less constant with pressure or Fe doping, but differs
greatly from that of pure MnSi at ambient pressure. We discuss the implications
of this ratio with respect to trends in the saturated magnetic moment and
helical pitch length as T_C \rightarrow 0 via doping and pressure,
respectively.
