Large enhancement of emergent magnetic fields in MnSi with impurities and pressure

We report a study of the topological Hall effect (THE) in Fe-doped MnSi and compare it 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 -> 0 via doping and pressure, respectively.