Muon-spin-rotation measurements in the ‘infinite-chain’ Ca2CuO3

We performed zero-field muon-spin-rotation measurements of the ‘infinite-chain’ compound Ca2CuO3. A spontaneous magnetic field is observed below 13 K. The exchange interaction inferred from susceptibility measurements and two-magnon Raman scattering is approximately 103 K, which implies a remarkable suppression of the ordering temperature (kBTN/J1d ∼ 0.01). We discuss the relevance of these measurements to the problem of one-dimensional spin 12 antiferromagnets.