NEUTRON-DIFFRACTION STUDY OF THE MAGNETIC-ORDERING IN BACUO2+X

Neutron-diffraction measurements have revealed that BaCuO2+x orders an tiferromagnetically below T-N = 15.0 +/- 0.5 K with a magnetic propaga tion vector kappa = [111]. The Cu atoms in the Cu-6 ring clusters, loc ated at the (1/4,1/4,1/4) positions, order ferromagnetically within th ese clusters while the clusters order antiferromagnetically. The magne tic moment of each of the ordered Cu atoms is (0.89 +/- 0.05)mu(B) at T = 4.2 K. No evidence of long-range magnetic ordering of the Cu atoms in the Cu-18 clusters,located at the (0,0,0) and (1/2,1/2,1/2) positi ons, was found down to a temperature T = 2.5 K.