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

Abstract

Abstract 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.