Upper critical fields up to 60 T and the vortex matter phase diagram of arsenic-deficient LaO0.9F0.1FeAs1-δ

We report resistivity, magnetization and upper critical field Bc2(T) data for arsenic deficient LaO0.9F0.1FeAs1-δ in a wide temperature and high field range up to 60 T. These disordered samples exhibit a slightly enhanced transition temperature of Tc = 29.0 K and a significantly enlarged slope dBc2/dT = -5.4 T/K near Tc. The high-field Bc2(T) data obtained from resistance measurements in pulsed magnetic fields follow up to about 30 T the WHH (Werthamer-Helfand-Hohenberg) curve for the orbital limited upper critical field, but show a clear flattening above 30 T. This flattening evidences Pauli limiting behavior (PLB) with Bc2(0) ∼ 63 T. We compare our results with Bc2(T) data reported in the literature for clean and disordered samples. Whereas clean samples show no PLB for fields below 70 T as measured so far, the hitherto unexplained flattening of Bc2(T) for applied fields H||ab observed for several disordered closely related systems is interpreted as a manifestation of PLB. The influence of the arsenic vacancies in LaO0.9F0.1FeAs1-δ on the vortex matter phase diagram is studied by magnetization measurements on bulk samples.