Superconductivity critical magnetic field

Three important characteristics of the superconducting state are the critical temperature, the critical magnetic field, and the critical current. These parameters can be varied by using different materials or giving them special metallurgical treatments. 

Superconductivity exists within the boundaries of three limiting parameters which must not be exceeded the critical temperature (T ), the critical magnetic field (H ) and the critical current demsity (J ). 

Table 6.1 Critical Temperature and Critical Magnetic Field of a Number of Superconducting Elements...

Figure 13.17 (a) Typical graph of critical magnetic field 3Cc as a function of temperature for a type I superconductor. Magnetic fields greater than 3tc suppress the superconducting transition, (b) Critical magnetic fields for several type I superconductors. 

Superconductivity is the absence of resistance to dc conduction this occurs only below a critical temperature Tc, a critical magnetic field (which is a function of T and current density j), and a critical current density j, which is a function of T and H. For alloys, does not exceed 23 -24 K (by contrast, some of the recently discovered ceramic high-Tc cuprate superconductors, such as HgBa2Ca2Cu30j , have Tc values as high as 140 K and can have comparable y c values), Designers of superconducting solenoid magnets... 

There are several dozen metallic AB2 compounds called Laves phases that are superconducting they have either cubic or hexagonal crystal structures. Some have critical temperatures above 10 K and high upper critical magnetic fields Bc2- For example, Zri/2Hfi/2V2 has rc = 10.1K, B 2 = 24 T, and a compound with a different Zr/Hf ratio has similar and Bc2 values with the critical current density Jc 4 X 10 A/cm. These materials also have the advantage of not being as hard and brittle as some other intermetallics and alloys with comparable transition temperatures. 

The preceding material may be used to characterize the thermodynamics of transitions from the normal to the superconducting state. This transformation takes place for a limited class of materials at a particular temperature Tc, currently below 140 K. For soft superconductors of type I this state is marked by a complete disappearance of electrical resistivity and by the fact that at moderate values the magnetic induction B = M. + AnH vanishes within the bulk of the sample, so that for such materials M = —AnH. However, as the field is increased a critical magnetic field He is reached beyond which the material reverts back to its normal state. In first approximation He depends only on temperature according to the relation... 

The critical magnetic-field strength He, for the second kind of superconductors, to which oxide HTSCs belong, it is the so-called upper critical field Hc2- At H > Hc2, the superconducting state disappears throughout the material bulk. 

Ho91b K. Holczer et ai, Critical Magnetic Fields in Os92a the Superconducting State of KaCeo, Phys. 

Critical Magnetic Fields in the Superconducting State of KaCeo K. Holczer ei al., Phps. Rev. Leii. 67, 271-274 (1991). 

The most distinguishing features of superconductive materials are the sudden and complete disappearance of electrical resistance below T, the high critical current density J ), which allows superconductors to conduct with no power loss and the high critical magnetic fields (H 2) in which superconductivity can exist. The relationship among these features is shown in Figure 3,... 

Superconductivity [1.35]. Timgsten is a Type I superconductor with a transition temperature of 0.0154 0.0005 K. The critical magnetic field strength -> 0) is 1.15 0.03Oe. (91.5 A-m ). Impurities only show a minor influence on the transition... 

Studies have continued on the intercalation of the alkaline-earth metals into lattices of the transition-metal sulphides. Calcium and strontium are intercalated into M0S2 from liquid ammonia solution. X-Ray data reveal a lowering of the crystal symmetry of the sulphide and an increase in the complexity of the structure on intercalation. The intercalation compounds begin to superconduct at ca 4 K (for Ca) and 5.6 K (for Sr), and they show considerable anisotropy with respect to the critical magnetic field. Calcium in liquid ammonia also intercalates with TiS2- Two Ca,TiS2 phases have been identified. The limits of the first are 0.03 0.50, for which a relationship between x and cell parameters a and c... 

We have analyzed a possible influence of the vortex lattice nascent process on the resistive characteristics of superconducting multilayered nanostructures with different geometrical symmetry. In order to achieve the temperature dependences of both the parallel and the perpendicular critical magnetic fields, we have considered... 

The following tables include superconductive properties of selected elements, compounds, and alloys. Individual tables are given for thin fUms, elements at high pressures, superconductors with high critical magnetic fields, and high critical temperature superconductors. 

TABLE 6. High Critical Magnetic-Field Superconductive Compounds and Alloys... 

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