Magnetic phase transition in the S=1/2 zigzag-chain compound SrCuO2

We have studied the magnetic properties of the S=1/2 quasi-one-dimensional Heisenberg antiferromagnet SrCuO2, which has zigzag chains of Cu2+ ions. We have observed a static magnetic ordering below T-c similar to 2 K. The weak internal field in the muon spin relaxation spectra and the absence of the magnetic Bragg peaks below T-c suggest that the Cu2+ moments are largely reduced probably due to the quantum fluctuation. The remarkable suppression of the ordering temperature (kT(c)/J(2)=1.1x10(-3)), where J(2) is the dominant exchange constant, probably originates from the combined effects of quantum fluctuation and frustration.