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A Study of Reversible and Irreversible Magnetization Behaviour in Conventional Superconductors

  • S. Ramakrishnan
  • Ravi Kumar
  • C. V. Tomy
  • A. K. Grover
  • S. K. Malik
  • P. Chaddah

Abstract

The complete expulsion of magnetic flux on cooling a superconductor in a dc magnetic field (Meissner-Oschenfeld effect) ensures that the magnetic response of a superconductor is reversible and that it is a thermodynamic property. Incomplete flux expulsion is, however, a common occurrence in both type I and type II superconductors and such materials display a path-dependent or hysteretic magnetic response. Detailed studies in the high temperature superconductors (HTSC) have resulted in the observation1 that there exists a thermodynamic reversible region in (H,T) space just below the normal-superconductor phase boundary (T c (H) line). Here H is the applied field, T is the temperature of the sample. Hysteretic behaviour sets in only below the irreversibility line, (T r , H r ), and different techniques have been used to determine this (T r,Hr) line in the HTSC. We have searched for such an irreversibility line in specimens of conventional type I and type II superconductors by both dc and ac magnetization techniques. The following four different procedures were employed to determine the (H r , T r ) line in HTSC:
  1. (a)

    Field-cooled (FC) and zero field-cooled (ZFC) magnetization curves in a constant dc field H were measured as a function of temperature. The temperature at which these merge [T r (H)] gives a point on the irreversibility line.

     
  2. (b)

    Hysteretic isothermal magnetizaton, i.e, M vs H, curves were measured where M is the sample’s magnetization per unit volume and H is the applied field. The field, [H r (T)], at which the hysteresis vanishes gives a point on the (T r , H r ) line.

     
  3. (c)

    The complex ac magnetic susceptibility (χ = χ′ H + iχ″ H ) was measured in constant dc field H as a function of temperature. A thermoaynamic response requires that χ′ H (T) be positive just below T c and this is called the Differential Paramagnetic Effect (DPE).2 The temperature at which χ′ H (T) switches from positive to negative is identified with T r (H).

     
  4. (d)

    From the simultaneous measurements of χ″ H (T) as a function of temperature in a constant dc field, the temperature at which it peaks is identified as T p (H).

     

Keywords

Hysteresis Loss Perpendicular Orientation Disc Plane Irreversibility Line Conventional Superconductor 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media New York 1991

Authors and Affiliations

  • S. Ramakrishnan
    • 1
  • Ravi Kumar
    • 1
  • C. V. Tomy
    • 1
  • A. K. Grover
    • 1
    • 2
  • S. K. Malik
    • 1
  • P. Chaddah
    • 1
    • 3
  1. 1.Tata Institute of Fundamental ResearchBombayIndia
  2. 2.Department of PhysicsPunjab UniversityChandigarhIndia
  3. 3.Bhabha Atomic Research CentreBombayIndia

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