Temperature dependence of the upper critical field of high-Tc   superconductors from isothermal magnetization data. Application to   polycrystalline samples and ceramics
  Using a recently developed scaling procedure that allows to establish the temperature dependence of the normalized upper critical field from measurements of the equilibrium isothermal magnetization, we analyze experimental data obtained on polycrystalline and ceramic samples. We show that the scaling procedure works quite well in all cases that we have considered. This provides a very strong evidence that the temperature dependencies of the normalized upper critical field are independent of the orientation of an applied magnetic field with respect to the crystallographic axes of these materials. 
I. L. Landau and H. R. Ott