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The effects of Sr substitution on the Ba site for Hg 0.7 Pb 0.3 Ba 2 Ca 2 Cu 3 O y superconductors were studied. The irreversibility line for the Sr-substituted compound is much steeper compared to the pristine sample. From the analysis of the reversible magnetization, we found that the fluctuation magnetization is much suppressed in the Sr-substituted compound, though the high-field magnetization data around T c (H) still displayed twodimensional scaling behavior. This feature can be explained by the enhanced interlayer coupling strength associated with the Sr substitution. Various thermodynamic parameters were obtained from the theoretical analysis. It is notable that the zero-temperature upper critical field H c 2 (0) of the Sr-substituted sample is about two times that of the nonsubstituted sample.

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