Investigation of Upper Critical Magnetic Field in Two‐Band Model for the Iron‐Based Superconductors Ca 0.83 La 0.17 FeAs 2 and Ca 0.8 La 0.2 Fe 0.98 Co 0.02 As 2

ABSTRACT This research work focuses on the theoretical investigation of upper critical magnetic field, lower critical magnetic field, Ginzburg–Landau coherence length and Ginzburg–Landau penetration depth using a two‐band model for the iron‐based superconductors and . Using the phenomenological Ginzburg–Landau free‐energy density functional formulated for a two‐band superconductor with two coupled superconducting order parameters, we derived analytical expressions for the temperature dependence of the upper, and lower critical magnetic fields, the angular dependence of the upper critical magnetic field, as well as the temperature dependence of the GL coherence length and penetration depth for both superconducting compounds. Phase diagrams corresponding to the relevant superconducting parameters are constructed and analyzed. The theoretical results are in good agreement with the experimental and theoretical observations, demonstrating that the two‐band GL formalism effectively captures the anisotropic superconducting behavior of these iron‐based systems. These findings provide deeper insight into multi‐band effects, anisotropy, and high‐field superconducting properties, supporting future studies on the design and optimization of iron‐based superconductors.