Samples of $\left({\mathrm{Mn}}_{1-x}{\mathrm{Co}}_x\right)\mathrm{Si}$ with $x=0.15$ and $x=0.17$ were grown, and their physical properties: magnetization, magnetic susceptibility, resistivity, and heat capacity were studied. The data analysis included previous results at $x=0.057,0.063,\mathrm{and}0.09$. The doping of MnSi with Co completely destroys the helical phase transition, but it saves the helical fluctuation area normally situated slightly above the phase-transition temperature. This area, spreading from $\sim 5$ to 0 K does not change much with doping and forms some sort of helical fluctuation cloud, revealing the quantum critical properties: $C_p/T\to \infty$ at $T\to 0$.

• Received 15 April 2022
• Revised 9 June 2022
• Accepted 30 June 2022

DOI:https://doi.org/10.1103/PhysRevB.106.014406