Magnetic phase transition in the S= zigzag-chain compoundSrCuO2

We have studied the magnetic properties of the S= quasi-one-dimensional Heisenberg antiferromagnet ${\mathrm{SrCuO}}_2$, which has zigzag chains of ${\mathrm{Cu}}^{2+}$ ions. We have observed a static magnetic ordering below ${\mathrm{T}}_{\mathrm{c}}$∼2 K. The weak internal field in the muon spin relaxation spectra and the absence of the magnetic Bragg peaks below ${\mathrm{T}}_{\mathrm{c}}$ suggest that the ${\mathrm{Cu}}^{2+}$ moments are largely reduced probably due to the quantum fluctuation. The remarkable suppression of the ordering temperature (${\mathrm{kT}}_{\mathrm{c}}$/${\mathrm{J}}_2$=1.1×${10}^{\mathrm{-}3}$), where ${\mathrm{J}}_2$ is the dominant exchange constant, probably originates from the combined effects of quantum fluctuation and frustration.