Induced magnetization in lithium doped YBa2Cu3Oy

• Published in: Journal of applied physics 1999-01, Vol.85 (2), p.1002-1009
• Main Authors: Maury, F., Nicolas-Francillon, M., Nanot, M., Ollitrault-Fichet, R.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.369221

The magnetization of two series of lithium doped YBCO samples, having Li molar concentrations ranging from 0 to 0.4, has been measured as a function of the magnetic field from 50 to −50 kOe at various temperatures between 5 and 30 K. The samples of the first series, annealed in oxygen, are orthorhombic and metallic. The samples of the second series, annealed in argon, are tetragonal and insulating. Above the transition temperature of the superconducting orthorhombic samples and up to 300 K, the magnetization is found to be quite similar for both series of samples, increasing with the lithium content of the sample and, in the tetragonal samples, increasing with the oxygen content of the sample. At low temperatures and for the tetragonal samples, the magnetization is found not to be proportional to the magnetic field as it should be if it were due to local moments of the order of μB. The value of 1.1μB obtained for the effective magnetic moment per Li ion from M(T) experiments carried out at H=10 kOe, which has been attributed to local moments carried by Cu ions neighboring a Li ion, may thus not have a straightforward interpretation. The shape of the M(H)curves, which exhibit a downturn at high fields, is reproduced well by the sum of a linear term and a Langevin function as if the samples displayed superparamagnetism. Some possible interpretations of this phenomenon are discussed.