ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Magnetic relaxation in ceramic cylindrical samples of BiPbSrCaCuO high Tc superconductors has been studied as a function of applied magnetic field for a constant decay rate of that field strength. We have analyzed the variation of the ac susceptibility versus time just after removing the magnetic field. Data have been obtained by means of an inductive technique from 1 to 3600 s, with magnetic fields that range from 10 to 100 Oe, and by switching off the field at a constant rate of 25 Oe/s. The field dependence of the thermally activated parameters has been obtained within the framework of the Anderson–Kim theory and using the so-called box distribution of energies. Anderson–Kim considered a logarithmic decay of the magnetic flux governed by an effective energy U=U0−FVX, where U0 is the pinning energy, V is the activation volume, X the pinning length, and F the driving force density. In this case we have found a field dependence of the form H−n for the pinning energy, with n close to 2 and temperature dependent. However, we have observed that the box distribution, which assumes the existence of a continuous energy spectrum, shows no field dependence for the effective energy. © 1996 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.361949
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