Competing Ordering Modes in the Distorted Quantum Kagome Material Clinoatacamite Cu 2 Cl ( OH ) 3

We have studied the magnetic properties of clinoatacamite Cu 2 Cl ( OH ) 3 , the parent compound of the quantum spin liquid candidate herbertsmithite and a long-standing puzzle among frustrated quantum magnets. As we reveal using density-functional theory, clinoatacamite belongs to the class of distorted kagome antiferromagnets with the kagome plane being embedded into a low-symmetry crystal structure. By means of thermodynamic measurements, muon spin rotation and relaxation, as well as neutron diffraction on single crystals, we find in zero magnetic field complex behavior below T I = 18.1 K which unfolds in three temperature regions I–III. We propose this complexity in multicritical clinoatacamite to arise from the competition of antiferromagnetic ordering modes from the underconstrained manifold of modes, which can lead to a metamagnetic texture in zero field.