Type 1 and type 2 superconductors: For one group of SUPERCONDUCTOR in which below Hc is in the Meissner state, where it excludes all the magnetic flux from the interior of the sample. Above Hc it is in normal state, where the magnetic flux penetrates the sample as it would normally and the conductivity is finite. The superconductor of this group is called Type 1 superconductor or soft superconductor. They are usually pure specimens of some elements and the value of critical magnetic field for them is always too low to have any useful technical applications in coils for super conducting magnets. They are completely diamagnetic and give away their super conductivity at lower field strength. For other groups of superconductors, the transition does not occur sharply from the Meissner state to the normal state, but goes through an intermediate phase. The applied field is able to pierce through certain local regions of the sample. As the applied field is below than Hc1, the specimen is diamagnetic and hence the flux is completely excluded in this range of field, it is called critical field. At this flux begins to penetrate the specimen and the penetration increases until Hc2 is reached. At Hc2 the magnetization vanishes and the specimen becomes normal conductor, Hc2 is called upper critical field. Moreover, the magnetization of this group of superconductors vanishes gradually as the field is increased rather than suddenly as for the Type 1 superconductors. However they are completely superconductors for all fields below Hc2. The superconductors of this group are called Type 2 superconductors or hard superconductors. They tend to be alloys or transition metals with high values of electrical resistivity in the normal state.
INTERMEDIATE STATE: When the specimen becomes super conductor the flux is concentrated at the sides of the specimen the initiation of the transition from superconducting state to normal state may exists as a complex mixture of normal and superconducting regions called the Intermediate state. The intermediate state is considered completely equivalent to a mixture of the two states.