Coexisting ferromagnetic order and disorder in a uniform system of hydroxyhalide Co2(OH)3Cl

Order or disorder often exists in a uniform spin system consisting of one kind of magnetic ion. Nevertheless, they rarely coexist in normal conditions. Our thermodynamic and microscopic magnetic studies of Co2(OH)3Cl, a distorted tetrahedral lattice compound with uniform Co2+ spin, demonstrate that the spins located on one corner of the tetrahedron are periodically ordered, but those on the other three are disordered below a ferromagnetic transition at TC=10.5K. The partial order resembles that of the field-induced "kagomé-ice" state in spin ice pyrochlore compounds. Evidence suggests that a distortion in the tetrahedron is responsible for this partial ferromagnetic order in a zero field.