Vortex pinning and magnetic phase diagram of EuRbFe4As4 iron-based superconductor

Abstract

We performed systematic AC susceptibility and magnetic moment measurements to investigate the vortex dynamics and pinning in single crystals as a function of temperature, frequency, and DC magnetic field. The vortex solid-liquid line was determined, and it can be fitted well with using β = 1.74 ± 0.1–1.91 ± 0.1, where Tp is the peak position on an imaginary part of the AC susceptibility plot (), for H ab. It indicates a rather high pinning strength of the vortex system. The activation energy U0 was determined from thermally activated flux creep theory and reached 6700 ± 1100 K at low fields, suggesting strong vortex pinning. A field dependence of U0(H ab) ∼ Ha with a = 0.47(4) suggests thermally activated plastic pinning or caused by planar defects. Magnetic moment measurements also confirmed strong pinning in the superconductor, and the superconducting response gives the main contribution to the M(H) hysteresis. Additionally, we show long-range ordering of the Eu2 + sublattice according to the AC susceptibility measurement data.