Creep properties of MgB2 bulk near the irreversibility line

Using susceptometric measurements at different frequencies and fields we in vestigate the creep properties of MgB2 near the irreversibility line. The d ata analysis allows to find the dependence of the pinning energy U on field and temperature. Remarkably, it turns out that the dependence on B and T c annot be separated as U(B, T) = U-0(B) f (T). An analysis aimed at understa nding the mechanisms underlying this lack of a scaling law is tried. Self-c onsistent experimental hints prove that different creep mechanisms are acti ve in low-frequency/low-field and high-frequency/high-field regions.