Three-Dimensional Anisotropic Fluctuation Diamagnetism Around the Superconducting Transition of Ba1-xKxFe2As2 Single Crystals in the Finite-Field (or Prange) Regime

The magnetization around the superconducting transition was recently measured in a high-quality Ba1-x K (x) Fe2As2 single crystal with magnetic fields applied along and transverse to the crystal Fe-layers [J. Mosqueira et al. in Phys. Rev. B 83:094519, 2011]. Here we extend this study to the finite-field (or Prange) regime, in which the magnetic susceptibility is expected to be strongly dependent on the applied magnetic field. These measurements are analyzed in the framework of the three-dimensional anisotropic Ginzburg-Landau (3D-aGL) approach generalized to the short-wavelength regime through the introduction of a total-energy cutoff in the fluctuation spectrum. The results further confirm the adequacy of GL approaches to describe the fluctuation effects close to the superconducting transition of these materials.