Antiferromagnetism in Li substituted YBa sub(2)Cu sub(3)O sub(y) studied by neutron powder diffraction measurements

The magnetic structure of two well characterised YBa sub(2)Cu sub(3-x)Li sub(x)O sub(y ) samples, with similar Li concentrations, x = 0.08-0.09, and slightly different oxygen concentrations, y = 6.06 and y = 6.18, has been studied by neutron powder diffraction measurements. The lithium substitution is found to induce a strong decrease of the Neel temperature and of the mean ordered magnetic moment on the Cu2 sites. T sub(N) is approximately 245 K for y = 6.06 instead of 415-400 K in unsubstituted YBa sub(2)Cu sub(3)O sub(y) with y = 6.0-6.2. The mean ordered moment at low temperature, mu sub(0)/ mu sub(B), is 0.33 plus or minus 0.03 for y = 6.06, and 0.17 plus or minus 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 possible mechanisms of the strong lithium effect are discussed. copyright 2001 Elsevier Science B.V.