Magnetization loops and non-scaling behavior of flux pinning force of Fe1+y Te1−x Se x studied by numerical simulation

Abstract

The magnetization of type-II superconductors has usually been described using the critical state models (CSMs). However, CSMs do not consider the time-dependent magnetic relaxation. In this work, to study the influence of magnetic relaxation on the magnetic hysteresis loops (MHLs), critical current density J c, and flux pinning force F p, a numerical method proposed by (Qin and Yao 1996 Phys. Rev. B 54 7536) was adopted and extended to the quasi-two-dimensional case. MHLs at different temperatures measured by using applied field with different sweeping rates can be well reproduced. The critical current density after relaxation J s, and F p can also fit the experimental results well. Based on the numerical simulation, the non-scaling behavior of field-dependent normalized pinning force has been proven to be due to the magnetic relaxation. By comparing the normalized pinning force with the Dew-Hughes model, the dominant pinning type in Fe1+y Te0.6Se0.4 has been confirmed to be the volume Δκ pinning. In addition, the second peak effect is found to be related to the flux lattice transition from elastic lattice to plastic lattice (E-P transition).