Magnetic effects induced by lithium in YBa2Cu3-xLixOz

Resistivity and magnetisation measurements were carried out on various seri es of lithium doped YBCO samples in extended oxygen and lithium concentrati on ranges in which the materials are single phase: 6 < O < 7 and 0 < x(Li) < 0.4. The materials are O7-type, i.e., orthorhombic and metallic when anne aled under oxygen; they are tetragonal and insulating when annealed under a rgon atmosphere, for the O-samples, a decrease of (1.02 +/- 0.12) oxygen mo le(-1) per Li+ is observed. All the O-samples show superconductivity at H = 30 G. The susceptibility data show that lithium gradually destroys either superconductivity (O-samples) or 3D antiferromagnetism (T-samples) and simu ltaneously localised moments appear since the (chi)(T) magnetic behaviour i s Curie-Weiss type. Tf the observed effective moment is assumed to be induc ed by lithium, this moment is constant and equal to (1.08 +/- 0.11) mu(B) p er Li as long as x < 0.4; moreover, it does not depend on the crystalline s tructure. This can be understood if the local structure around the lithium site is always O6-type, whatever the structure is. (C) 1999 Elsevier Scienc e B.V. All rights reserved.