It is well known that superconductivity is suppressed by the presence of magnetic ions in the conventional metallic superconductors. This phenomenon can be understood in terms of the pair-breaking mechanism. On the other hand, the existence of some magnetic rareearth metallic superconductors has been explained by claiming that the superconductivity and the magnetism take place in different parts of the crystal, with little interaction between the two. However, in all high-Tc ceramic superconductors, the CuO2 planes which contain magnetic Cu2+ ions probably enhance the superconductivity, instead of degrading it [1]. One can conclude that, in most cases, the substitution of “native” ions by foreign ions leads to a transition from superconductivity to antiferromagnetism or vice versa. The real coexistive cases of the phenomena are rare [2] and controversial, mainly because of the question of homogenity of the samples. However, it seems quite clear that whenever substitution decreases the number of charge carriers (either holes or electrons) the superconductivity is suppressed.

In copper oxide superconductors, it has now been well established that the superconducting properties are related to the hole concentration [3, 4]. Tarascon et al.[5], studied various substitutions of the rare-earths into Bi4Sr4Ca2− xRxCu4Oy (x≥ 1) and reported that for x= 1.5 the compounds became semiconducting. At low doping (x≤ 0.5) Tc was not