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MAGNETIC PROPERTIES OF CRYOGENIC MATERIALS

MAGNETIC PROPERTIES OF CRYOGENIC MATERIALS. www.spectrose.com. Topics. Magnetic Properties Paramagnetism Diamagnetism Superconductivity Meissner Effect Change in Properties. www.spectrose.com. Magnetic Properties.

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MAGNETIC PROPERTIES OF CRYOGENIC MATERIALS

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  1. MAGNETIC PROPERTIES OFCRYOGENIC MATERIALS www.spectrose.com

  2. Topics • Magnetic Properties • Paramagnetism • Diamagnetism • Superconductivity • MeissnerEffect • Change in Properties www.spectrose.com

  3. Magnetic Properties • The magnetic moment of a system measures the strength and the direction of its magnetism. The term itself usually refers to the magnetic dipole moment. • Anything that is magnetic, like a bar magnet, or a loop of electric current can have their own magnetic moments.  • There are many different magnetic properties: Paramagnetic, Diamagnetic, Ferromagnetic, Ferromagnetic, etc... www.spectrose.com

  4. Paramagnetism • Paramagnetism is a form of magnetism whereby certain materials are attracted by an externally applied magnetic field. • Have a positive magnetic susceptibility. • Paramagnetic material does not retain the magnetic properties when the external field is removed. • Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. www.spectrose.com

  5. Diamagnetism • The property of an object or material that causes it to create a magnetic field in opposition to an externally applied magnetic field. • Adiamagnet is not a permanent magnet. • Diammagnetic materials get repelled by magnetic field. • Eg: Zinc www.spectrose.com

  6. Superconductivity • The simultaneous disappearance of all electric resistance and the appearance of perfect diamagnetism. • Appears only at low temperature. • Transition temperature – The temperature at which superconductivity occurs in the absence of magnetic field. • Superconductivity can be destroyed by increasing the magnetic field to critical field. www.spectrose.com

  7. Superconductivity…..(cndn) • Type 1 superconductors have single value of critical field. • Type 2 super conductors have ‘Lower & Upper Critical fields. • Type 1 materials obey Silsbee hypothesis which highlight the relevance of the term critical current. www.spectrose.com

  8. Meissner Effect • Proposed by Meissner and Ochsenfeld in 1933. • Experiment is done in a monocrystal of tin. • The magnetic flux density in a super conducting bulk material is always zero. • Magnetic field is expelled when the material become a superconductor. • Basis of the frictionless bearing and superconducting motor. www.spectrose.com

  9. Meissner Effect.. (cndn) www.spectrose.com

  10. Change in Properties • Specific Heat increase abruptly. • Thermoelectric Effects (Thomson, Seeback & Peltier) vanishes. • Thermal conductivity of pure metals decreases abruptly and for some alloys (Eg. Pb-Bi), it increases. • Electric Resistance decreases to Zero abruptly for Type 1 and for Type 2, change occurs in 1 K temperature range. • Magnetic Perimiabilitysuddenly bcames Zero for Type 1 and for Type 2, Meissner effect is incomplete for magnetic fields greater than Lower Critical Fields. www.spectrose.com

  11. Thank You.. www.spectrose.com

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