We present the first report on a large low-temperature magnetoresistance (MR) of more than 1600% in a SrFe2As2 single crystal and 1300% in a low-energy Ca ion-implanted SrFe2As2 single crystal that occurs before the emergence of crystallographic stra
in-induced bulk superconductivity arising from a sample aging effect. In accordance to band structure calculations from literature, which consitently show more than 2 bands are involved in the transport, we have modeled this large MR at high fields using a 3-carrier scenario rather than solely on quantum linear MR model generally used to explain the MR in iron-pnictides. At and below 20 K the large MR may be due to 3-carrier transport in an inhomogeneous state where there are superconducting and metallic regions.
Polycrystalline Sr1-xNdxFeAsF samples were prepared at various Nd-doping levels using both a stoichiometric mixture of the starting materials and in slight excess amounts of FeAs. Susceptibility and resistivity of the samples were studied down to 4 K
revealing a probable coexistence of superconductivity and a magnetic ordering. Temperature dependence of resistivity for all the Nd-doped samples shows the presence of a transition below 15 K most likely originating from the magnetic ordering of Nd moments, while the spin-density-wave anomaly at 175 K survives up to 0.35 Nd-doping. Superconductivity only occurs above 0.40 Nd-doping with onset maximum Tc reaching as high as 52 K.
The transport properties, upper critical fields, superconducting anisotropy, and critical current density in an iso-valent phosphorus-doped BaFe2As2 single crystal close to optimum doping are investigated in this report. Temperature dependent resisti
vity and susceptibility show a superconducting transition temperature, Tc, just below 31 K both with sharp transitions. The upper critical field parallel to the ab-plane, Hc2^ab, is above 77 Tesla while that along the c-axis direction, Hc2^c, is just above 36 Tesla, yielding a low superconducting anisotropy ratio ~ 2. The estimated inter-plane coherence length based on the Ginzburg-Landau (G-L) theory indicates BaFe2(As0.68P0.32)2 is still above the point for a dimensional crossover inferring the superconducting layers are not weakly-coupled in this system. The critical current density at 5 K obtained from magnetization loops measurement show a modest Jc as high as 10^5 A/cm2.
