Physical properties of MnSi at extreme doping with Co: Quantum criticality

Samples of $({\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Co}}_x)\mathrm{Si}$ 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 $x=0.057,0.063,\phantom{\rule{0.28em}{0ex}}\mathrm{and}\phantom{\rule{0.28em}{0ex}}0.09$. 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 $\ensuremath{\sim}5$ to 0 K does not change much with doping and forms some sort of helical fluctuation cloud, revealing the quantum critical properties: ${C}_p/T\ensuremath{\rightarrow}\ensuremath{\infty}$ at $T\ensuremath{\rightarrow}0$.