Vortex dynamic, pinning and irreversibility field investigation in EuRbFe4As4 superconductor

We performed systematic AC susceptibility and magnetic moment measurements to investigate the vortex dynamics and pinning in the $EuRbFe_4As_4$ single crystal as a function of temperature, frequency, and DC magnetic field. The vortex solid-liquid line was determined and it fits well with $H(T_p)=H_0(1-t_p)^β$ using $β$=1.74-1.91, for $H\parallel ab$. It indicates a rather high pinning strength of the vortex system. The activation energy $U_0$ was determined from thermally activated flux creep theory and reached 6700 K at low fields, suggesting strong vortex pinning. A field dependence of $U_0(H\parallel ab)\sim H^a$ with $a=0.47$ suggests thermally activated plastic pinning or caused by planar defects. Magnetic moment measurements also confirmed strong pinning in a $EuRbFe_4As_4$ superconductor and the superconducting response gives the main contribution to the $M(H)$ hysteresis. Additionally, we found evidence of long-range magnetic interactions in $Eu^{2+}$ sublattice and the FM-like nature of $Eu^{2+}$ atoms ordering.

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