Vanishing vortex creep at the transition from ordered to disordered vortex phases in Ba${}_{0.64}$K${}_{0.36}$Fe${}_2$As${}_2$

Abstract

By measuring the dynamical and conventional magnetization relaxation of the Ba${}_{0.64}$K${}_{0.36}$Fe${}_2$As${}_2$ single crystals, we found strong second peak effect on the magnetization hysteresis loops. It is found that there is a kink of magnetization at a field between the valley and maximum magnetization. Interestingly, the magnetization relaxation rate has a deep minimum at the field with the kink, indicating a diminished vortex creep. The relaxation rate at this field is clearly smaller than the so-called universal lower limit of the relaxation rate characterized by ($S_0\approx G{i}^{1/2}(T/T_{\mathrm{c}}$). This diminished vortex creep is associated with the origin of the SMP effect and attributed to the strongly hindered flux motion when experiencing the transition from the quasi-ordered to disordered vortex phases.

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