Dear Youssef Ait Ahmed,

I need some further information before I can try to answer this question.

Looking forward to your answer.

Dear Sir Ger Koper,

I want to thank you sir for your answer, this curve show the M (H) in the superconductor compound ( diamagnetic ). Hc is the thermodynamic magnetic field.

Dear Youssef Ait Ahmed

My response consisted of 2 questions, it was not an answer. I repeat with 2 questions.

Looking forward to your answers,

Dear Sir Ger Koper,I want to thank you again.

1)The measured of the M (H) was obtained by using a commercial conducting quantum interference device (SQUID).

2)reference:Article

I would thank you with the best regards. 

Dear Youssef Ait Ahmed

In response to your answers:

1. You seem to imply that you have no clue how the instrument does it. I do urge you to figure out, there may be important assumptions in the procedure that affect the way you analyze the data.

2. Thanks for the article. The "thermodynamic magnetic field" is just what I would call the local field, i.e. the field the spins "feel", so corrected for demagnetization effects. If I understand the article well, the procedure to determine Hc1 is classical, there are many descriptions on the web.

But, and this is why I stress point 1, the accuracy of the measurement of the low field magnetization will determine the quality of the result. Funny low field values as in your graph may just screw up the analysis you are after.

Ger