Glassy relaxation and weak vortex pinning in anisotropic (Ca_0.85La_0.15)₁₀(Pt₃As₈)(Fe₂As₂)₅ single crystals

We present a comprehensive study on the vortex dynamics of (Ca_0.85La_0.15)₁₀(Pt₃As₈)(Fe₂As₂)₅ ​ single crystals, characterized by magnetization measurements. With a superconducting critical temperature of 32 K, this material is notable for its substantial anisotropy (5–6), which significantly influences the intrinsic vortex fluctuations. Our results reveal low critical current densities, i. e. J_c∼0.6 MA/cm² at 1.8 K and low magnetic fields. The magnetic field dependences of J_c exhibit a fishtail or second peak in the magnetization, a feature commonly associated with weak vortex pinning and vortex relaxation crossovers. Moreover, the flux creep rates are exceptionally large at low fields and temperatures. Through Maley's analysis, we extract low vortex pinning energies (∼50 K) and glassy exponents that are consistent with expectations for single-vortex pinning, progressively evolving towards vortex bundles. These findings enhance our understanding of vortex dynamics in iron-based superconductors, highlighting the key role of intrinsic vortex fluctuations in the vortex phase diagram.