352 research outputs found
Surface Hardening of Ni Alloys by Means of Plasma Ion Nitriding (PIN) Process (Report II) : Effect of Alloying Elements on Surface Hardening(Materials, Metallurgy & Weldability)
^{31}P and ^{75}As NMR evidence for a residual density of states at zero energy in superconducting BaFe_2(As_{0.67}P_{0.33})_2
^{31}P and ^{75}As NMR measurements were performed in superconducting
BaFe_2(As_{0.67}P_{0.33})_2 with T_c = 30 K. The nuclear-spin-lattice
relaxation rate T_1^{-1} and the Knight shift in the normal state indicate the
development of antiferromagnetic fluctuations, and T_1^{-1} in the
superconducting (SC) state decreases without a coherence peak just below T_c,
as observed in (Ba_{1-x}K_{x})Fe_2As_2. In contrast to other iron arsenide
superconductors, the T_1^{-1} \propto T behavior is observed below 4K,
indicating the presence of a residual density of states at zero energy. Our
results suggest that strikingly different SC gaps appear in
BaFe_2(As_{1-x}P_{x})_2 despite a comparable T_c value, an analogous phase
diagram, and similar Fermi surfaces to (Ba_{1-x}K_{x})Fe_2As_2.Comment: 4 pages, 5 figure
Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe(AsP)
We present a comprehensive overview of vortex pinning in single crystals of
the isovalently substituted iron-based superconductor
BaFe(AsP), a material that qualifies as an
archetypical clean superconductor, containing only sparse strong point-like
pins [in the sense of C.J. van der Beek {\em et al.}, Phys. Rev. B {\bf 66},
024523 (2002)]. Widely varying critical current values for nominally similar
compositions show that flux pinning is of extrinsic origin. Vortex
configurations, imaged using the Bitter decoration method, show less density
fluctuations than those previously observed in charge-doped
Ba(FeCo)As single crystals. Analysis reveals that the
pinning force and -energy distributions depend on the P-content . However,
they are always much narrower than in Ba(FeCo)As, a
result that is attributed to the weaker temperature dependence of the
superfluid density on approaching in
BaFe(AsP). Critical current density measurements and
pinning force distributions independently yield a mean distance between
effective pinning centers nm, increasing with
increasing P-content . This evolution can be understood as being the
consequence of the P-dependence of the London penetration depth. Further
salient features are a wide vortex free "Meissner belt", observed at the edge
of overdoped crystals, and characteristic chain-like vortex arrangements,
observed at all levels of P-substitution.Comment: 11 page
Nematic magnetoelastic effect contrasted between Ba(FeCo)As and FeSe
To elucidate the origin of nematic order in Fe-based superconductors, we
report a Raman scattering study of lattice dynamics, which quantify the extent
of -symmetry breaking, in BaFeAs and FeSe. FeSe possesses a
nematic ordering temperature and orbital-related band-energy
split below that are similar to those in BaFeAs, but
unlike BaFeAs it has no long-range magnetic order. We find that the
phonon-energy split in FeSe sets in only well below , and
its saturated value is substantially smaller than that in BaFeAs.
Together with reported results for the Ba(FeCo)As family,
the data suggest that magnetism exerts a major influence on the lattice.Comment: 4 pages, 4 figure
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