Antiferromagnetism in Li substituted YBa2Cu3Oy studied by neutron powder diffraction measurements

The magnetic structure of two well characterized YBa2Cu3-xLixOy samples, with similar Li concentrations, x=0.08-0.09, and slightly different O concentrations, y=6.06 and y=6.18, has been studied by neutron powder diffraction measurements. Li substitution induces a strong decrease of the Neel temperature and of the mean ordered magnetic moment on the Cu2 sites. TN is 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, m0/mB, is 0.33plus/minus 0.03 for y=6.06, and 0.17plus/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 Li effect are discussed. 26 refs.