  We reanalyze the magnetization data collected on
Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+y) samples (Kim at al, Phys. Rev. B 72, 64525
(2005)) and argue that the method, which was used for the analysis of
equilibrium magnetization data, is not adequate to the experimental situation.
As a result, the temperature dependencies of the upper critical field Hc2(T)
and the magnetic field penetration depth lambda (T), obtained in this work, are
misinterpreted. Using a different approach to analysis, we demonstrate that the
normalizedHc2(T) curves are rather different from those presented in the
original publication and do not follow predictions of the
Werthamer-Helfand-Hohenberg theory. Another important observation is that the
Hc2(T) dependencies for two samples with different levels of doping are
qualitatively different.
