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Bauer, A.; Neubauer, A.; Franz, C.; M̈unzer, W.; Garst, M.; Pfleiderer, C. 
Quantum Phase Transitions in Single-Crystal ${\text{Mn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}\text{Si}$ and ${\text{Mn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{Si}$: {{Crystal}} Growth, Magnetization, Ac Susceptibility, and Specific Heat 
We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of Mn1-xFexSi and Mn1-xCoxSi for temperatures down to $\sim$2 K and magnetic fields up to 9 T. The suppression of the helimagnetic transition temperature T1 above a critical composition x1, as seen in the magnetization, ac susceptibility, and specific heat, suggests the existence of a quantum phase transition at x1. A Vollhardt invariance at a temperature T2$>$T1, which may be attributed to the Dzyaloshinsky-Moriya (DM) spin-orbit interactions, is also suppressed with increasing x and vanishes above a concentration x2, where x2$>$x1. When suppressing the effects of the DM interactions in an applied magnetic field, the magnetization for sufficiently large fields shares the signatures expected of an underlying putative ferromagnetic quantum critical point for a critical concentration xc, where x1$<$xc$<$x2. As a function of normalized concentration x/xc, where xCoc$\approx$0.084 and xFec$\approx$0.192, the properties of Mn1-xFexSi and Mn1-xCoxSi are essentially identical with x1/xc$\approx$0.78 and x2/xc$\approx$1.17. Taken together, our study identifies Mn1-xFexSi and Mn1-xCoxSi as model systems in which the influence of DM interactions on ferromagnetic quantum criticality may be studied. 
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Physical Review B 
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