Effect of Ge substitution on magnetic properties in the itinerant chiral magnet MnSi

We have investigated the effect of Ge substitution on the magnetic ordering in the B20 itinerant chiral magnet MnSi prepared by melting and annealing under ambient pressure. From a metallurgical survey, the solubility limit of Ge was found to be x=0.144(5) with annealing temperature Tan=1073 K. Magnetization measurements on MnSi1-xGex samples show that the helical ordering temperature Tc increases rapidly in the low-x range, whereas it becomes saturated at higher concentration x>0.1. The Ge substitution also increases both the saturation magnetization Ms and the critical field to the fully polarized state Hc2. In contrast to the saturation behavior of Tc, those parameters increase linearly up to the highest Ge concentration investigated. In the temperature-magnetic field phase diagram, we found enlargement of the skyrmion phase region for large x samples. We, furthermore, observed the nonlinear behavior of helical modulation vector k as a function of Ge concentration, which can be described qualitatively using the mean field approximation.