High-quality single crystal of Ca 0.8 La 0.2 Fe 0.98 Co 0.02 As 2 has been successfully synthesized using a self-flux method. The magnetization measurement reveals a second peak effect and high critical current density c J exceeding 2  10 6 A/cm 2 at 5 K (self-field). The upper critical field anisotropy was systematically studied by measuring the electrical resistivity under various magnetic fields and angles. The angle-dependent magnetoresistance, by choosing an appropriate anisotropy parameter within the framework of the anisotropic Ginzburg-Landau (AGL) theory, can be scaled onto one single curve. In the normal state, the negative Hall coefficient shows strong but nonmonotonic T-dependence through a minimum at ~175 K.Moreover, it is shown that the magnetoresistance apparently violates the semiclassical Kohler's rule below ~ 175 K but can be well scaled by the Hall angle instead. This suggests either the change of carriers with T or the exotic anisotropic scattering in the system. Keywords: iron based superconductor, critical current density, upper critical field anisotropy, Hall effect and magnetoresistance

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Fe 1 + y Te0.6Se0.4 has considerable application potential due to its large critical current density (J c) and high upper critical magnetic field ( H c2 ). However, the uncertainty of the anisotropy of J c and the unclear flux-pinning mechanism have limited the application of this material. In this study, the J c in three directions were obtained from magnetic hysteresis loop measurements. A large anisotropy of J c a b / J c c ∼ 10 was observed, and the origin of the anisotropy was discussed in details. Flux pinning force densities (F p) were obtained from J c, and a non-scaling behavior was found in the normalized pinning force f p [ F p / F p-max ] versus the normalized field h[H/ H c2 ]. The peaks of pinning force shift from a high h to a low h with increasing temperature. Based on the vortex dynamics analysis, the peak shift was found to originate from the magnetization relaxation. The J c and F p at critical states free from the magnetic relaxation were regained. According to the Dew-Hughes model, the dominant pinning type in Fe 1 + y Te0.6Se0.4 clean single crystals was confirmed to be normal point pinning.

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