High-Field Pauli-Limiting Behavior and Strongly Enhanced Upper Critical   Magnetic Fields near the Transition Temperature of an Arsenic-Deficient   LaO_0.9F_0.1FeAs_(1-\delta) Superconductor
  We report upper critical field B_c2(T) data for disordered (arsenic-deficient) LaO_0.9F_0.1FeAs_(1-delta) in a wide temperature and magnetic field range up to 47 T. Because of the large linear slope of Bc2 about -5.4 T/K to -6.6 T/K near Tc = 28.5 K the T-dependence of the in-plane Bc2(T) shows a flattening near 23 K above 30 T which points to Pauli-limited behavior with Bc2(0) about 63-68 T. Our results are discussed in terms of disorder effects within conventional and unconventional superconducting pairings. 
G. Fuchs, S.-L. Drechsler, N. Kozlova, G. Behr, A. Koehler, J. Werner,   K. Nenkov, C. Hess, R. Klingeler, J.E. Hamann-Borre...