Spin-liquid ground state in the frustrated kagome antiferromagnet MgCu3(OH)6Cl2

We report muon spin resonance experiments on MgxCu4-x(OH)(6)Cl-2 with x similar to 1, a material isostructural to Herbertsmithite exhibiting regular kagome planes of S = 1/2 ions (Cu2+), and therefore a candidate for a spin-liquid ground state. We evidence the absence of any magnetic ordering down to 20 mK (similar to J/10(4)). We present a detailed investigation of the spin dynamics on well-characterized samples in zero and applied longitudinal fields, and a defect-based interpretation is proposed to explain the unconventional dynamics observed in the quantum spin-liquid phase.