Type I and Type II Superconductors

In type I superconductors, magnetization curve is as shown:They are completely diamagnetic or exhibits complete Meissener effectup to critical field Hc. They are also called soft superconductors.The Hc value for Type I superconductors are found to be very low.Hence it is not used for the construction of superconducting magnets.Eg: Al, In, Sn, Pb etc.In type II superconductors, magnetization is as shown:For applied fields below Hc1 the specimen is diamagnetic, exhibitingcomplete Meissner effect. Hc1, the flux begins to penetrate thespecimen and the penetration increases until Hc2 is related. HereMeissner effect is incomplete and the specimen is said to be in avertex (mixed) state. At Hc2, the specimen becomes a normal conductor.Hc2 is called upper critical field. They are also called hardsuperconductors. Hc2 value is larger than (may be even 100 times) theHc value for type I superconductors. Hence they are used in theconstruction of superconducting magnets. Eg: Nb3Sn, Nb3Ge etc.