Quantum Griffiths phase in disordered Mn1−xFexSi

We show the presence of magnetic rare regions consistent with the quantum Griffiths phase in Fe-doped MnSi using detailed heat capacity, magnetization, and muon spin relaxation (\ensuremath{\mu}SR) measurements down to millikelvin temperatures. The slow dynamics of these rare regions at low temperatures leads to the non-Fermi-liquid behavior in heat capacity and magnetization. The \ensuremath{\mu}SR and magnetization results further indicate that the dynamics freezes into a cluster-glass state below ${T}_f\ensuremath{\sim}1.25$ K. The results are in agreement with theoretical models proposed in the literature for metallic systems with Heisenberg symmetry that exhibit the quantum Griffiths phase in the presence of strong disorder.