Influences of quenching treatment and cobalt-doping on the thermally activated flux-flow behavior in KCa2(Fe1-xCox)4As4F2

Owing to the unique double-FeAs-layered structure between neighboring insulating layers, the 12442-type Fe-based superconductors are expected to host rich vortex phenomena in the mixed state. Here, we report a systematic investigation on the influences of quenching treatment and cobalt-doping on the magnetic vortex dynamics of KCa2(Fe1-xCox)(4)As4F2 (x = 0, 0.1) single crystals via electrical transport measurements. It is found that the slopes of the upper critical field near T-c, d(mu 0)H/dT|(Tc) along both directions (H perpendicular to c and H parallel to c), are doubled by the cobalt-doping with x = 0.1. The activation energy is acquired by analyzing the Arrhenius plots, which shows a H-alpha dependence with a change in the exponent alpha at around 3 T, indicating the evolution of the dominant pinning mechanisms in different field regions. Importantly, the quenching treatment obviously enhances the magnitude of activation energy and critical current density J(c), which can be suppressed by the introduction of cobalt-doping. Possible mechanisms for such evolutions of these important parameters are discussed. Our results emphasize the important role of quenching treatment in enhancing the activation energy and critical current density in 12442 system.