We have synthesized CaKFe 4 As 4 single crystals by a simple one-step method. X-ray analysis suggests that the single crystals are c-axis orientation and no obvious impurity phase can be detected. The onset transition temperature is about 35 K with the ΔT c ∼1 K. By measuring the magnetoreistance, the vortex liquid-to-glass transitions of the CaKFe 4 As 4 single crystals have been investigated. The effective flux pinning potential U 0 (B, T) and well scaling of the resistivity r(B, T) were achieved. The vortex phase diagrams have been established on the basic of vortex glass temperature T g and upper critical field H c2 . We have compared the vortex glass phase diagram of CaKFe 4 As 4 with Ba 1−x K x Fe 2 As 2 single crystals, and found that both samples have narrow vortex liquid region. The analysis on flux pinning indicates that the flux pinning ability of CaKFe 4 As 4 is very strong and only slightly smaller than Ba 1−x K x Fe 2 As 2 single crystals. The dependence of flux pinning energies U B of CaKFe 4 As 4 on magnetic induction is U B µ B −0.265 and B −0.177 for the H//c and H//ab, respectively. Taking the structural difference between CaKFe 4 As 4 and Ba 1−x K x Fe 2 As 2 into account, the origin of the flux pinning in CaKFe 4 As 4 may have close relationship with itself electronic inhomogeneity and accompanying nanosizedintercalation of CaFe 2 As 2 as well as distorted FeAs 4 -tetrahedrons.

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