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The surprisingly rapid relaxation of the sustainable current density in thecritical state of single crystalline Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ isinvestigated for magnetic fields oriented parallel to the c-axis and to the$ab$--plane respectively. Due to the inadequacy of standard analysis proceduresdeveloped for flux creep in the high temperature superconducting cuprates, wedevelop a simple, straightforward data treatment technique that reveals thecreep mechanism and the creep exponent $\mu$. At low magnetic fields, below thesecond magnetization peak, $\mu$ varies only slightly as function oftemperature and magnetic flux density $B$. From the data, we determine thetemperature- and field dependence of the effective activation barrier forcreep. At low temperatures, the measured current density approaches thezero--temperature critical current density (in the absence of creep) to withina factor 2, thus lending credence to earlier conclusions drawn with respect tothe pinning mechanism. The comparable values of the experimental screeningcurrent density and the zero-temperature critical current density reveals thelimited usefulness of the widely used "interpolation formula".

Vortex creep and critical current densities in superconducting (Ba,K)Fe$_{2}$As$_{2}$ single crystals