Onset of a skyrmion phase by chemical substitution in MnGe-based chiral magnets

We study the evolution of the magnetic phase diagram of Mn1-xFexGe alloys with concentration x (0 <= x <= 0.3) by small-angle neutron scattering. We unambiguously observe the absence of a skyrmion (Sk) lattice (or A phase) in bulk MnGe and its onset under a small Mn/Fe substitution. The A phase is there endowed with extremely small Sks, potentially resulting in a high density, and is stabilized within a very large temperature region and a field range which scales with the Fe concentration. Our findings highlight the possibility to fine tune the properties of skyrmion lattices by means of chemical doping.