Doping evolution of magnetization hysteresis in (Ba1-xKx)Fe2As2 single crystals: Crossover from the second magnetization peak to peak effect

Magnetic hysteresis loops (MHLs) have been systematically measured in a series of (Ba1-xKx)Fe2As2 single crystals from underdoped x$=$0.177 to end member x$=$1 with applied magnetic fields parallel to c axis (H//c). The second magnetization peak (SMP) or fishtail effect was observed within the doping range 0.177$\le $x$\le $0.650. Remarkably, with further increasing doping the SMP becomes narrow and emerges very close to the irreversible field (Hirr) for the samples 0.692$\le $x$\le $0.910. The similar peak effect (PE) had been widely observed in various conventional or low Tc superconductors. Meanwhile, the magnetization curves change from symmetrical to asymmetric hysteresis loops, which suggests a dominant surface pinning instead of bulk pinning in the samples. Our findings demonstrate that (Ba1-xKx)Fe2As2 system is a very unique system that that links the SMP and PE by its doping dependence. Our results will lead to a better understanding of the underlying mechanisms for the origin of the SMP and PE.