Coexistence of long-range order and spin fluctuation in geometrically frustrated clinoatacamite Cu2Cl(OH)3.

Cu. Below 6.5 K, the static long-range order transforms abruptly into ametastable state with nearly complete depolarization of muon spins which suggests strong fluctuation. Thesystem then enters a state in which partial long-range order and spin fluctuation coexist down to the lowestexperimentally attainable temperature of 20 mK. This work presents a novel system for studyinggeometric frustration.