Magnetization and ac susceptibility study of the cubic chiral magnet Mn1-xFexSi

We present a comprehensive and systematic magnetization and ac susceptibility study of Mn1-xFexSi over an extensive range of ten Fe concentrations between x=0 and x=0.32. With increasing Fe substitution, the critical temperature decreases but the magnetic phase diagrams remain qualitatively unaltered for x≤x∗≈0.11 with clear boundaries between the helical, conical, and skyrmion lattice phase as well as an enhanced precursor phase. A notably different behavior sets in for x=0.11,0.13, and 0.14, where certain characteristics of helimagnetic correlations persist, but without clear phase boundaries. Although a qualitative change already sets in at x∗, the transition temperature and spontaneous magnetization vanish only at xc=0.17 where also the average magnetic interactions change sign. Although the Curie-Weiss temperature reaches -12 K for x=0.32, no signature of long-range magnetic order is found down to the lowest temperature, indicating a possible significant role for quantum fluctuations in these systems. © 2018 American Physical Society.