Dinesh,

What you are describing is a magnetization measurement result. The demagnetizing factor depends upon the shape of the sample in a strong manner. I suggest that you do the measurement on a reproducible and controlled shape of sample and then measure the demagnetization of the unknown and compare it with that of a known superconductor taken well below Tc using the same sample shape and apparatus.

This will give you a better feel than attempting to do things in this manner as ZFC and FC are subject to the consideration of just how far from Hc1 you are and is the material a type II or type I material (I include weakly linked heterogenous grain boundary connected materials as type II, this is not strictly correct but behaviorly similar enough).

One other concern is the sample size -- it must be significantly larger than the penetration depth.....

Hope this helps,

Grover Larkins

Dear Dinesh,

I agree with the observations of G. Larkins, about the relevance of demagnetizing factor, measuring down to temperatures well below Tc and having sample size much larger then the penetration depth.  However, a good estimate of Meissner fraction can also be made using the usual type of magnetization measurements (ZFC and FC), paying attention to the following:  1) Use a smallest possible value of applied field (e.g. H ~ 5 or 10 Oe), this will ensure staying below Hc1 at  T

Dear Dinesh,

O.F. de Lima is correct, I would only add that the sample thickness must be at least 10 times the penetration depth.

Of course, if the sample is unknown, the FC/ZFC method is of limited utility as the penetration depth and, whether or not, it is a heterogenously connected set of weak links is also unknown as is Hc1. For very thin samples (small in any dimension in relationship with the penetration depth IN THAT DIMENSION's direction)  Hc1 becomes depressed and may actually go to zero, despite the field strength used to measure it. That is always worth noting when dealing with very small sample volumes with uncertain (and for the High Tc materials, LARGE) penetration depths. The penetration depth for Nb is 39nm and for YBCO it is 150nm in the ab plane and 800nm in the c direction. Note the difference; if your sample size was nbased on the Nb penetration depth you would be totally out of luck using that assumption in a mixed YBCO impure sample to get the SC volume.....

All the best,

Grover

The Meissner effect is obtained by coolig in a dc field as small as possible.

It is 100% for very good superconductors (type 1 without defect, or type 2 without pinning). In fact, the field can be trapped by defects during the cooling, which results into a reduced meissner effect.

The shielding effect,is measured after zero field cooling, and applying a very small field (