Alternating Magnetic Shielding and Resistivity in High Critical Temperature Superconductors (Y \(_{1-x}\) Ln \(_x\) )SrBaCu \(_3\) O \(_{6+\delta }\) (x \(=\) 0, 5 and 1, Ln \(=\) rare earth)

Since its discovery in early 1986 [1], research has been directed toward the study of high critical temperature (T \(_c\) ) superconducting cuprates. The alternating magnetic susceptibility ( \( \chi _{ac} = \chi ' + i\chi ''\) ) is very useful for characterizing high-T \(_c\) superconductors. This technique is used to study the flux dynamics of superconductors. In the real part ( \( \chi '\) ), just below the critical temperature T \(_c\) , a strong decrease in its amplitude is a consequence of diamagnetic shielding. While in the imaginary part ( \( \chi ''\) ), the \(T_p\) peak represents the alternating losses. It is well known that high-T \(_c\) superconductivity is carried by holes in the CuO \(_2\) planes, where the holes exhibit strong correlations among themselves. These planes are sensitive and influenced by many factors such as radius, valence, and distribution of surrounding ions and oxygen content. Moreover, the ion distribution is strongly influenced by thermal treatments applied during sample preparation. The charge transfer mechanisms in HTSCs [2] present peculiarities stipulated by the manifestation of a series of specific phenomena observed in the normal (non-superconducting) state. In general, the physical properties of these compounds are closely linked to their preparation conditions.