الفهرس 
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Abstract
Theoretically, Abrikosov [7] investigated the properties of superconductors in external magnetic fields. In 1957, he discovered that superconducting materials can be classified into two groups namely Type I and Type II superconductors [8]. The superconductor materials that called Type I superconductors are totally exclude an applied magnetic flux for H ≤ Hc and its magnetization M reduced to zero, figures 1.4(a) and 1.5(a), respectively. On the other hand, Type II superconductors have two different critical magnetic fields named as the lower critical magnetic field Hc1 and the upper critical magnetic field Hc2, as shown in figure 1.4(b). When the applied field (H < Hc1), type II behaves like type I below Hc. Whereas in the mixed or vortex state (Hc1 < H < Hc2), the flux penetrates partly into the material in the form of thin normal cylinders and its magnetization gradually decreased, figure 1.5(b). As the field increases above Hc2, the flux totally penetrates the whole sample, and it returns to the normal-state. The fundamental difference between these two types is that the coherence length ξ, which is a characteristic size of the Cooper pair wave-function, in type I superconductors is longer than the London magnetic penetration depth λ while ξ is smaller than λ in type II materials.