Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$

Abstract

We report the studies of detailed magnetic relaxation and isothermal magnetization measurements in the vortex state of the 112-type iron-pnictide Ca 0.82 La 0.18 Fe 0.96 Ni 0.04 As 2 superconductor with T c ∼ 22 K. In the isothermal M (H), a well defined second magnetization peak (SMP) feature is observed in the entire temperature range below T c for measurements with H c-axis. However, for H ab-planes, the SMP feature is suppressed at low temperatures, which might be due to 2D Josephson vortices forming at low temperatures and high magnetic fields in such an anisotropic system. A rigorous analysis considering the magnetic relaxation data for H c-axis suggests an elastic to plastic pinning crossover across H p , which also seems accompanied with a possible phase transition in vortex lattice near H p . Moreover, point disorder and surface defects are likely to be the dominant sources of pinning, which contribute to the δl-type of pinning in the sample. A high J c , in access of 10 5 A/cm 2 observed could potentially make this material technologically important.