Near-T vortex pinning and Dew–Hughes scaling in CaK(Fe1−xNix)4As4 and Ba(Fe1−xCox)2As2 single crystals

Abstract

We compare pinning-force scaling in Fe-based superconductors exhibiting moderate vortex fluctuations using the Dew-Hughes formalism. Single crystals of CaK(Fe1−xNix)4As4 (1144) and Ba(Fe1−xCox)2As2 (122) are analyzed by fitting the normalized pinning force, , as a function of the reduced field near Tc, with the peak position at . In 1144, data are well described by single-peak scaling with h0 ≃ 0.30–0.34, consistent with predominant point-like disorder. In 122, h0 shifts from ≈ 0.17–0.23 in underdoped crystals and to ≈ 0.37–0.40 near optimal doping, indicating a mixed δTc/point pinning landscape. Literature datasets show that proton irradiation in lightly doped 1144 preserves a single peak near h0 ≈ 0.33, whereas heavy-ion irradiation in near-optimally doped 122 produces a high-field shoulder. Overall, Dew-Hughes scaling captures the main trends phenomenologically and provides a practical map linking the effective peak position h0 to the prevailing pinning landscape.