Flux pinning and the vortex phase diagram in optimized CaKFe4As4 single crystals fabricated by a one-step method

Abstract

We have synthesized CaKFe4As4 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 ΔTc ∼ 1 K. By measuring the magnetoreistance, the vortex liquid-to-glass transitions of the CaKFe4As4 single crystals have been investigated. The effective flux pinning potential U0(B, T) and well scaling of the resistivity (B, T) were achieved. The vortex phase diagrams have been established on the basic of vortex glass temperature Tg and upper critical field Hc2. We have compared the vortex glass phase diagram of CaKFe4As4 with Ba1−xKxFe2As2 single crystals, and found that both samples have narrow vortex liquid region. The analysis on flux pinning indicates that the flux pinning ability of CaKFe4As4 is very strong and only slightly smaller than Ba1−xKxFe2As2 single crystals. The dependence of flux pinning energies UB of CaKFe4As4 on magnetic induction is UB B−0.265 and B−0.177 for the H//c and H//ab, respectively. Taking the structural difference between CaKFe4As4 and Ba1−xKxFe2As2 into account, the origin of the flux pinning in CaKFe4As4 may have close relationship with itself electronic inhomogeneity and accompanying nanosized-intercalation of CaFe2As2 as well as distorted FeAs4-tetrahedrons.