Abstract:
The focus of this project was to prepare and study the magnetic
and transport properties of oriented, polycrystalline high T,
superconductors, with special emphasis on their anisotropy. it had
further been planned that the behavior of the magnetic flux, (so called
vortices) would be analyzed in terms of the dynamics of these entities,
subjected to the thermal and anisotropic conditions. During the period of
this grant proposal, we have been able to achieve almost all the goals
envisaged in the proposal. These are illustrated by the 10 publications
directly related to the project, which have been published in quality
international journals during this period. (List attached). We have also
produced two Ph.D. theses in superconductivity during this period, one
of which was submitted by the Research Officer, supported by this
project.
We have prepared very good quality melt textured high TT
superconductors, which were required for performing the studies on
anisotropy of the magnetization of these materials. We have also
conducted and published the dc and ac magnetization studies of these
-materials focusing on the properties of the vortices and obtained an
understanding of the factors limiting the critical currents in various
crystallographic directions. We have also studied in detail the dynamics
of vortex motion in these materials by the methods of magnetic
relaxation, field sweep rate dependence and ac susceptibility in
superposed dc fields. Our studies have enabled us to draw a
comprehensive picture that the barriers to vortex motion, and
subsequent dissipation, are lowered in dc fields and in particular in
crossed ac and dc fields the effects are drastic. We have also found that
the decrease in critical currents with increasing fields can be explained
on the basis of the so-called Critical state model for fields applied parallel
to the c-axis, while the behavior perpendicular to the same is quite
different. We have conducted transport measurements and identified the
role of the (JxB) force as well as an angle independent, phase slip
contribution to the dissipation. Our studies therefore constitute part of
the major international effort to determine the electrodynamics of
layered, anisotropic superconductors, the mechanisms determining the
losses, and the anisotropy of their response.
