3 research outputs found
Comparative High Field Magneto-Transport of Rare Earth Oxypnictides with Maximum Transition Temperatures
The recent discovery of a new class of superconducting oxypnictides with high
transition temperatures may have profound implications for understanding
unconventional high-temperature superconductivity. Like the cuprates, the
oxypnictides seem to manifest an interleaving of charge donor and
superconducting layers emerging upon doping of an antiferromagnetic parent
semi-metal. Here we report magneto-transport measurements of three rare earth
(Re = La, Nd, Sm) oxypnicide compounds with the transition temperatures near
the maximum reported to date, in very high DC and pulsed magnetic fields up to
45 and 54 T, respectively. Our resistivity, Hall coefficient and critical
magnetic fields data suggest that these oxypnictide superconductors bridge the
gap between MgB and YBaCuO as far as electromagnetic and vortex
properties are concerned.Comment: 6 pages, 3 figure
Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides
Early studies have found quasi-reversible magnetization curves in
polycrystalline bulk rare-earth iron oxypnictides that suggest either
wide-spread obstacles to intergranular current or very weak vortex pinning. In
the present study of polycrystalline samarium and neodymium rare-earth iron
oxypnictide samples made by high pressure synthesis, the hysteretic
magnetization is significantly enhanced. Magneto optical imaging and study of
the field dependence of the remanent magnetization as a function of particle
size both show that global currents over the whole sample do exist but that the
intergranular and intragranular current densities have distinctively different
temperature dependences and differ in magnitude by about 1000. Assuming that
the highest current density loops are restricted to circulation only within
grains leads to values of ~5 MA/cm2 at 5 K and self field, while whole-sample
current densities, though two orders of magnitude lower are 1000-10000 A/cm2,
some two orders of magnitude higher than in random polycrystalline cuprates. We
cannot yet be certain whether this large difference in global and intragrain
current density is intrinsic to the oxypnictides or due to extrinsic barriers
to current flow, because the samples contain significant second phase, some of
which wets the grain boundaries and produces evidences of SNS proximity effect
in the whole sample critical current.Comment: 28 pages, 14 figure