S. Katrych

Single crystals of superconducting SmFeAsO1−xFy grown at high pressure

Single crystals of SmFeAsO1-xFy of a size up to 120 micrometers have been grown from NaCl/KCl flux at a pressure of 30 kbar and temperature of 1350-1450 C using the cubic anvil high-pressure technique. The superconducting transition temperature of the obtained single crystals varies between 45 and 53 K.Obtained crystals are characterized by a full diamagnetic response in low magnetic fields and by a high critical current density in high magnetic fields. Structural refinement has been performed on single crystal. Differential thermal analysis investigations at 1 bar Ar pressure show decomposition of SmFeAsO1-xFy at 1302 C.Single crystals of SmFeAsO1−xFy of a size up to 120 × 100 µm2 have been grown from NaCl/KCl flux at a pressure of 30 kbar and temperature of 1350–1450 °C using the cubic anvil high-pressure technique. The superconducting transition temperature of the obtained single crystals varies between 45 and 53 K. Obtained crystals are characterized by a full diamagnetic response in low magnetic fields and by a high critical current density in high magnetic fields. Structural refinement has been performed on the single crystal. Differential thermal analysis investigations at 1 bar Ar pressure show decomposition of SmFeAsO1−xFy at 1302 °C.

Tuning the superconducting and magnetic properties of Fe y Se 0.25 Te 0.75 by varying the iron content

The superconducting and magnetic properties of FeySe0.25Te0.75 single crystals (0.9≤y≤1.1) were studied by means of x-ray diffraction, superconducting quantum interference device magnetometry, muon-spin rotation, and elastic neutron diffraction. The samples with y<1 exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for y≥1 but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the FeySe1−xTex can be tuned not only by varying the Se/Te ratio but also by changing the Fe content. ©2010 The American Physical Society

High-pressure flux growth, structural, and superconducting properties ofLnFeAsO (Ln=Pr, Nd, Sm) single crystals

Single crystals of the LnFeAsO (Ln1111, Ln = Pr, Nd, and Sm) family with lateral dimensions up to 1 mm were grown from NaAs and KAs flux at high pressure. The crystals are of good structural quality and become superconducting when O is partially substituted by F (PrFeAsO1−xFx and NdFeAsO1−xFx) or when Fe is substituted by Co (SmFe1−xCoxAsO). From magnetization measurements, we estimate the temperature dependence and anisotropy of the upper critical field and the critical current density of underdoped PrFeAsO0.7F0.3 crystal with Tc ≈ 25 K. Single crystals of SmFe1−xCoxAsO with maximal Tc up to 16.3 K for x ≈ 0.08 were grown. From transport and magnetic measurements, we estimate the critical fields and their anisotropy and find these superconducting properties to be quite comparable to the ones in SmFeAsO1−xFx with a much higher Tc ≈ 50 K. The magnetically measured critical current densities are as high as 109 A/m2 at 2 K up to 7 T, with indication of the usual fishtail effect. The upper critical field estimated from resistivity measurements is anisotropic with slopes of ∼−8.7 T/K (H||ab plane) and ∼−1.7 T/K (H||c axis). This anisotropy (∼5) is similar to that in other Ln1111 crystals with various higher Tcs.

Th-substituted SmFeAsO: Structural details and superconductivity with Tc above 50 K

We report structural, magnetic, and transport properties of polycrystalline samples and single crystals of superconducting Sm1−xThxFeAsO with maximal Tc above 50 K, prepared under high pressure. Bulk superconducting samples do not undergo a structural phase transition from tetragonal to orthorhombic symmetry at low temperatures. The unit-cell parameters a and c shrink with Th substitution and the fractional atomic coordinate of the As site zAs remains almost unchanged while that of Sm/Th zSm/Th increases. Upon warming from 5 to 295 K the increase in the FeAs layer thickness is dominant, while the changes in the other structural building blocks are minor, and they compensate each other, since the As-Sm/Th distance contracts by about the same amount as the O-Sm/Th expands. The polycrystalline and single-crystalline samples are characterized by a full diamagnetic response in low magnetic field, by a high intergrain critical current density for polycrystalline samples, and by a critical current density on the order of 8×105 A/cm2 for single crystals at 2 K in fields up to 7 T. The magnetic penetration depth anisotropy γλ increases with decreasing temperature, in a similar way to that of SmFeAsO1−xFy single crystals. The upper critical field estimated from resistance measurements is anisotropic with slopes of ∼5.4 T/K (H∥ab plane) and ∼2.7 T/K (H∥c axis), at temperatures sufficiently far below Tc. The low-temperature upper critical field anisotropy γH is in the range of ∼2, consistent with the tendency of a decreasing γH with decreasing temperature, previously reported for SmFeAsO1−xFy single crystals. © 2010 The American Physical Society

Superconductivity at 23 K and low anisotropy in Rb-substituted BaFe2As2 single crystals

Single crystals of

Quasiparticle relaxation dynamics in spin-density-wave and superconducting SmFeAsO1−xFx single crystals

{\text{Ba}}_{1\ensuremath{-}x}{\text{Rb}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}

Evidence for Two Distinct Anisotropies in the Oxypnictide Superconductors SmFeAsO0.8F0.2 and NdFeAsO0.8F0.2

with

Local Quasiparticle Density of States of Superconducting SmFeAsO1 xFx Single Crystals: Evidence for Spin-Mediated Pairing

x=0.05\ensuremath{-}0.1

Conventional superconductivity and hysteretic Campbell penetration depth in single crystals MgCNi3

have been grown from Sn flux and are bulk superconductors with

Influence of Mg deficiency on crystal structure and superconducting properties in MgB2 single crystals

{T}_{c}