IRREVERSIBILITY_FIELD_AND_PINNING_POTENTIAL___________________________________________

                             IN_Bi-2212_SUPERCONDUCTING_SINGLE_CRYSTAL________________________________________



                 T._Hirano______, T. Matsushita, Y. Nakayama*, J. Shimoyama* and K. Kishio*

          Department of Computer Science and Electronics, Kyushu Institute of Technology,

                                        680-4 Kawazu, Iizuka 820-8502, JAPAN

                             *Department of Superconductivity, University of Tokyo,

                               7-3-1 Hongo, Bunkyou-ku, Tokyo 113-8654, JAPAN



    Pinning  potential  is  an  important  parameter  which  determines  the  pinning  characteristics  of

superconductors such as the irreversibility field and the relaxation rate of a persistent current.  Al-

though the irreversibility field and the relaxation rate have been discussed in detail, the discussion

has  been  given  separately  on  each  characteristic  and  any  comprehensive  discussion  has  not  yet

been given.  In this paper, we try to explain the both characteristics from the pinning potential.

The specimen is an overdoped superconducting Bi-2212 single crystal prepared by a floating zone

method and the critical temperature is 78.3 K. The irreversibility field and the relaxation of DC

magnetization  are  measured  using  a  SQUID  magnetometer.  The  pinning  potential  is  estimated

from the relaxation rate using the theoretical result of Welch.  The irreversibility field is calculated

from the obtained pinning potential using the flux creep theory and the result is compared with

the experiment.