Geometric frustration in a new material system M2X(OH)3

Muon spin relaxation/rotation (μSR) are carried out on a new magnetic system of M2X(OH)3 (M=transition metal, X=halogen), which we show to be a new geometric frustration system for d-electron spins. Contrasting behaviors were observed for clinoatacamite Cu2Cl(OH)3 and Co2Cl(OH)3. Clinoatacamite Cu2Cl(OH)3 undergoes antiferromagnetic transition at T N=18 K with distinct muon spin rotations, and then it transforms abruptly into a metastable state with nearly complete depolarization of muon spins which suggests strong fluctuation. The system then enters a state in which partial long-range order and spin fluctuation coexist down to the lowest experimentally attainable temperature of 20 mK. For Co2Cl(OH)3, although dynamic interactions exist at temperatures higher than 400 K, static order only forms at a much lower temperature of T C=10 K with coexistence of spin fluctuation. This work demonstrates the coexistence of long-range order and spin fluctuation in a novel system of d-electron transition metal oxides