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-dimensi onal 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 an d the absence of the magnetic Bragg peaks below T-c suggest that the C u2+ moments are largely reduced probably due to the quantum fluctuatio n. The remarkable suppression of the ordering temperature (kT(c)/J(2)= 1.1x10(-3)), where J(2) is the dominant exchange constant, probably or iginates from the combined effects of quantum fluctuation and frustrat ion.