Superconductor magnets

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. 

Kamerlingh Onnes, at the University of Leiden, discovered superconductivity in 1911. He found that the resistance of some metallic wires became zero at very low temperature it did not just approach zero, there was no dissipation of heat. At that time his laboratory was the only one equipped for studies at the temperature of liquid He (bp 4.1 K). Theoretical explanations of the phenomenon did not appear until the work of John Bardeen, Leon Cooper, and Robert Schrieffer in 1957. They received the Nobel Prize in Physics in 1972. The expense and difficulty of applying superconductivity to practical problems limits the applications. Nevertheless, superconductor magnets of very high field are now widely used in NMR in chemistry and the medical diagnostic applications of NMR called MRI (magnetic resonance imaging—they wanted to avoid the word "nuclear ). 

Magnetic materials are not superconductors Magnetism and superconductivity appear to be mutually exclusive. In fact, doping of magnetic impurity usually destroys superconductivity. 

Keywords High-Tc superconductors, magnetic properties, the t-J model. 

Gadolinium 64 Gd Electronic materials, high-temperature refractories, alloys, cryogenic refrigerant, thermal neutron absorber, superconductor, magnetic materials, bubble memory substrates... 

In recent years, new permanent magnets have come on the market. They are made of an alloy of iron, neodymium and boron. They exhibit strong stable fields. They are strong enough that they have displaced superconductor magnets in some classes of medical magnetic resonance machines. Their use... 

Part k covering functional materials is organized in a two-step approach. The first step corresponds to searching for the substance of interest, that is, the relevant group of substances. The second step corresponds to the physical property of interest. Materials covered are semiconductors, superconductors, magnetic materials, dielectrics and electrooptics, and ferro- and antiferroelectrics. 

Although several other types of exotic superconductors (e.g., organic superconductors, heavy-fermion f-electron superconductors, magnetically ordered superconductors, multinary rare-earth, actinide, and transition-metal superconductors) have been investigated intensely since 1986, the cuprate superconductors have received by far the most attention because the highest values of the superconducting critical temperature are found in this class of materials. Rare-earth and actinide elements are key constituents of many of the high-temperature cuprate superconductors and have played a prominent role in the development of the first and some of the more important cuprate superconductors. 

Cardarelli, F. 2008. Materials Handbook A Concise Desktop Reference, 2nd ed. London/ New York Springer-Verlag. This book is divided into 14 families of materials (e.g., metals and alloys, semiconductors, superconductors, magnetic and electrical materials, ceramics). Physico-chanical properties are supplied for each class of materials in tabular form. Emphasis is given to the most conunon industrial materials in each class. A bibliography is included. Available online on SpringerLink. 

For type I superconductors, magnetic field exclusion is complete below a critical field, and field penetration is complete once He is exceeded. This penetration is gradual with increasing magnetic field for type II materials. 

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