Anisotropic critical current density and flux pinning mechanism of Fe 1+y Te0.6Se0.4 single crystals

Fe1+yTe0.6Se0.4 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)(ab)/T-c(c) similar to 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/Fp-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 Fe1+yTe0.6Se0.4 clean single crystals was confirmed to be normal point pinning.