Low-Dimensional Magnetism in Namibite Cu(BiO)₂VO₄OH

A synthetic analog of rare secondary mineral namibite Cu(BiO)(2)VO4OH has been obtained by the hydrothermal method. The crystal structure of this compound contains isolated uniform chains of vertex-connected copper-oxygen octahedra. Magnetic susceptibility (chi) and magnetization (M) measurements have not indicated the long-range order in the temperature interval 2-300 K. Specific heat (C-p) measurements suggest the formation of a spin-liquid state at low temperatures. X-band electron paramagnetic resonance data recorded at low temperatures have demonstrated only a signal from impurities. First-principles calculations have estimated the exchange interaction in the chains as J = 555 K, whereas exchange interactions between the chains turn out to be one to two orders of magnitude smaller. Thus, namibite represents a rare example of an unordered half-integer spin chain.