18 research outputs found
High - Temperature Superconductivity in Iron Based Layered Compounds
We present a review of basic experimental facts on the new class of high -
temperature superconductors - iron based layered compounds like REOFeAs
(RE=La,Ce,Nd,Pr,Sm...), AFe_2As_2 (A=Ba,Sr...), AFeAs (A=Li,...) and FeSe(Te).
We discuss electronic structure, including the role of correlations, spectrum
and role of collective excitations (phonons, spin waves), as well as the main
models, describing possible types of magnetic ordering and Cooper pairing in
these compounds.Comment: 43 pages, 30 figures, review talk on 90th anniversary of Physics
Uspekh
Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50K superconductor
We report an easy single step synthesis route of title compound
NdFeAsO0.80F0.20 superconductor having bulk superconductivity below 50 K. The
title compound is synthesized via solid-state reaction route by encapsulation
in an evacuated (10-3 Torr) quartz tube. Rietveld analysis of powder X-ray
diffraction data shows that compound crystallized in tetragonal structure with
space group P4/nmm. R(T)H measurements showed superconductivity with Tc (R=0)
at 48 K and a very high upper critical field (Hc2) of up to 345 Tesla. Magnetic
measurements exhibited bulk superconductivity in terms of diamagnetic onset
below 50 K. The lower critical field (Hc1) is around 1000 Oe at 5 K. In normal
state i.e., above 60 K, the compound exhibited purely paramagnetic behavior and
thus ruling out the presence of any ordered FeOx impurity in the matrix. In
specific heat measurements a jump is observed in the vicinity of
superconducting transition (Tc) along with an upturn at below T=4 K due to the
AFM ordering of Nd+3 ions in the system. The Thermo-electric power (TEP) is
negative down to Tc, thus indicating dominant carriers to be of n-type in
NdFeAsO0.80F0.20 superconductor. The granularity of the bulk superconducting
NdFeAsO0.8F0.2 sample is investigated and the intra and inter grain
contributions have been individuated by looking at various amplitude and
frequencies of the applied AC drive magnetic field.Comment: 26pages text + Figures: comments/suggestions welcome
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