Antiferromagnetism in Li substituted YBa2Cu3Oy studied by neutron powder diffraction measurements

The magnetic structure of two well characterised YBa2Cu3-xLixOy samples, wi th similar Li concentrations, I = 0.08-0.09, and slightly different oxygen concentrations, y = 6.06 and y = 6.18, has been studied by neutron powder d iffraction measurements. The lithium substitution is found to induce a stro ng decrease of the Neel temperature and of the mean ordered magnetic moment on the Cu2 sites. T-N is approximate to 245 K for y = 6.06 instead of 415- 400 K in unsubstituted YBa2Cu3Oy with y = 6.0-6.2. The mean ordered moment at low temperature, mu (0)/mu (B), is 0.33 +/- 0.03 for y = 6.06, and 0.17 +/- 0.08 for y = 6.18, instead of 0.64 in unsubstitued YBCO. These measured values are compared with other data from the literature and the various po ssible mechanisms of the strong lithium effect are discussed. (C) 2001 Else vier Science B.V. All rights reserved.