Upper critical field and peak effect in (Li0.8Fe0.2)OHFeSe single crystal

Abstract The transport properties, magnetization and dynamic magnetization relaxation rate measurements of (Li0.8Fe0.2)OHFeSe single crystals are presented at various magnetic fields and temperatures. The temperature dependence of upper critical field Hc2 exhibits an upward curvature. The Hc2 has been determined based on the orbital limiting and the Pauli limiting effect. The peak effect occurs in both the magnetic hysteresis loops and critical current density, which associates with the vortex motion. The field dependence of ∆M measured at different field sweeping rates is distinguished, which indicates a giant vortex creep. The magnetic relaxation rate Q has been investigated, indicating a transition between the two different vortices motion with increasing field. Our results suggest that the peak effect originates from the vortex transition from the elastic motion to the plastic motion.