A novel Kagome uud-ddu spin order in Heisenberg spin-1/2 Clinoatacamite Cu₄(OH)₆Cl₂, the parent compound of Herbertsmithite

The newly identified field-induced up-up-down order in Ba₃CoSb₂O₉ etc. renewed attention on exotic phases in spin-1/2 triangular-lattice antiferromagnets. Here, we report a unique zero-field noncoplanar up,up,down, down,down,up Kagome spin order in spin-1/2 antiferromagnet Clinoatacamite, Cu₄(OH)₆Cl₂, which consists of weakly-coupled Kagome layers and was known as the parent compound for the most researched spin liquid candidate Herbertsmithite ZnCu₃(OH)₆Cl₂. The two-dimensional uud-ddu Kagome order develops below T_N1 = 18.1 K in Clinoatacamite before a further transition into a three-dimensional magnetic order at low temperatures below T_N2 6.4 K with persistent spin fluctuations. The present work reveals a new unpredicted Kagome order in a readily accessible temperature range in the parent compound of a well-studied spin liquid. In addition, it has also solved a puzzling issue for a mysterious magnetic phase.