Zahlenwerte und Funktionen aus Naturwissenschaften und Technik Von Landolt-Bornstein. Neue Serie. Gesamtherausgabe: K. H. Hellwege. Gruppe II: Atom- und Molekularphysik. Band 1: Magnetische Eigenschaften freier Radikale. Von H. Fischer. Herausgeber: K. H. Hellwege und A. M. Hellwege. Pp. x + 154. (Berlin: Springer-Verlag, 1965.) 68 D.M.

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Electron Spin Resonance

We report synthesis and superconductivity at 3.7 K in PrO0.5F0.5BiS2. The newly discovered material belongs to the layered sulfide based REO0.5F0.5BiS2 compounds having a ZrCuSiAs-type structure. The bulk polycrystalline compound is synthesized by the vacuum encapsulation technique at 780 ∘C in a single step. Detailed structural analysis has shown that the as synthesized PrO0.5F0.5BiS2 is crystallized in a tetragonal P4/nmm space group with lattice parameters a=4.015(5) A, c=13.362(4) A. Bulk superconductivity is observed in PrO0.5F0.5BiS2 below 4 K from magnetic and transport measurements. Electrical transport measurements showed superconducting transition temperature (Tc) onset at 3.7 K and Tc(ρ=0) at 3.1 K. The hump at Tc related to the superconducting transition is not observed in the heat capacity measurement and rather a Schottky-type anomaly is observed at below ∼6 K. The compound is slightly semiconducting in a normal state. Isothermal magnetization (MH) exhibited typical type II behavior with a lower critical field (Hc1) of around 8 Oe.

Synthesis and Superconductivity of New BiS2 Based Superconductor PrO0.5F0.5BiS2

We study the pairing symmetry of a two-orbital J1-J2 model for FeAs layers in oxypnictides. We show that the mixture of an intraorbital unconventional s_{x;{2}y;{2}} approximately cos(k_{x})cos(k_{y}) pairing symmetry, which changes sign between the electron and hole Fermi surfaces, and a very small d_{x;{2}-y;{2}} approximately cos(k_{x})-cos(k_{y}) component is favored in a large part of the J1-J2 phase diagram. A pure s_{x;{2}y;{2}} pairing state is favored for J2>J1. The signs of the d_{x;{2}-y;{2}} order parameters in the two different orbitals are opposite. While a small d_{xy} approximately sin(k_{x})sin(k_{y}) interorbital pairing coexists in the above phases, the intraorbital d_{xy} pairing is not favored even for large J2.

http://absimage.aps.org/image/MAR09/MWS_MAR09-2008-001927.pdf

Pairing Symmetry in a Two-Orbital Exchange Coupling Model of Oxypnictides

A very recent report on the observation of superconductivity in Bi(4)O(4)S(3) [Mizuguchi, Y.; http://arxiv.org/abs/1207.3145] could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here the synthesis of Bi(4)O(4)S(3) at 500 °C by a vacuum encapsulation technique and its basic characterizations. The as-synthesized Bi(4)O(4)S(3) was contaminated with small amounts of Bi(2)S(3) and Bi impurities. The majority phase was found to be tetragonal (space group I4/mmm) with lattice parameters a = 3.9697(2) A and c = 41.3520(1) A. Both AC and DC magnetization measurements confirmed that Bi(4)O(4)S(3) is a bulk superconductor with a superconducting transition temperature (T(c)) of 4.4 K. Isothermal magnetization (M-H) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H(c1)) at 2 K for the new superconductor was found to be ~15 Oe. Magnetotransport measurements showed a broadening of the resistivity (ρ) and a decrease in T(c) (ρ = 0) with increasing magnetic field. The extrapolated upper critical field H(c2)(0) was ~31 kOe with a corresponding Ginzburg-Landau coherence length of ~100 A . In the normal state, the ρ ~ T(2) dependence was not indicated. Hall resistivity data showed a nonlinear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as-synthesized Bi(4)O(4)S(3). On the other hand, Bi heat-treated at the same temperature is not superconducting, thus excluding the possibility of impurity-driven superconductivity in the newly discovered superconductor Bi(4)O(4)S(3).

Bulk superconductivity in bismuth oxysulfide Bi4O4S3.

We report a strategy to induce superconductivity in the BiS$_2$-based compound LaOBiS$_2$ Instead of substituting F for O, we increase the charge-carrier density (electron dope) via substitution of tetravalent Th$^{+4}$, Hf$^{+4}$, Zr$^{+4}$, and Ti$^{+4}$ for trivalent La$^{+3}$ It is found that both the LaOBiS$_2$ and ThOBiS$_2$ parent compounds are bad metals and that superconductivity is induced by electron doping with \emph{T$_c$} values of up to 285 K The superconducting and normal states were characterized by electrical resistivity, magnetic susceptibility, and heat capacity measurements We also demonstrate that reducing the charge-carrier density (hole doping) via substitution of divalent Sr$^{+2}$ for La$^{+3}$ does not induce superconductivity

Superconductivity induced by electron doping in the system La1-xMxOBiS2 (M = Ti, Zr, Hf, Th)

Appearance of superconductivity in layered LaO0.5F0.5BiS2

Here, we report the synthesis and characterization of sulphur-substituted iron telluride i.e. FeTe 1− x S x ; ( x  = 0–30 %) system and study the impact of low temperature oxygen (O 2 ) annealing as well. Rietveld analysis of room temperature X-ray diffraction (XRD) patterns shows that all the compounds are crystallized in a tetragonal structure (space group P 4/ nmm ) and no secondary phases are observed. Lattice constants are decreased with increasing S concentration. The parent compound of the system i.e. FeTe does not exhibit superconductivity but shows an anomaly in the resistivity measurement at around 78 K, which corresponds to a structural phase transition. Heat capacity C p ( T ) measurement also confirms the structural phase transition of FeTe compound. Superconductivity appears by S substitution; the onset of superconducting transition temperature is about 8 K for FeTe 0.75 S 0.25 sample. Thermoelectric power measurements S ( T ) also shows the superconducting transition at around 7 K for FeTe 0.75 S 0.25 sample. The upper critical fields H c 2 (10%), H c 2 (50%) and H c 2 (90%) are estimated to be 400, 650 and 900 kOe respectively at 0 K by applying Ginzburg Landau (GL) equation. Interestingly, superconducting volume fraction is increased with low temperature (200 °C) O 2 annealing at normal pressure. Detailed investigations related to structural ( XRD ), transport [ S ( T ), R ( T ) H ], magnetization (AC and DC susceptibility) and thermal [ C p ( T )] measurements for FeTe 1− x S:O 2 system are presented and discussed.

Superconductivity and thermal properties of sulphur doped FeTe with effect of oxygen post annealing

One of the most important properties of very recently reported FeSe based superconductors is the robustness of their superconductivity under applied magnetic field. The synthesis and control of superconductivity in FeSe based compounds is rather a difficult task. Synthesis and physical property characterization for optimized superconductivity of FeSe1/2Te1/2 at 13 K is reported here. The compound crystallized in a tetragonal structure with lattice parameters a=3.8015(2) and c=6.0280(4) A. Magnetization measurements indicated bulk superconductivity with lower critical field (Hc1) of around 180 Oe. By applying Ginzburg–Landau theory, the Hc2(0) value is estimated to be ∼1840 kOe for the 90% of resistive transition. A heat capacity measurement revealed bulk superconductivity by a hump at Tc near 13 K and an expected decrease in the same was observed under an applied magnetic field.

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Synthesis and physical properties of FeSe1/2Te1/2 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 T
 c
 (R = 0) at 48 K and a very high upper critical field (H
 c2) of
up to 345 T. Magnetic measurements exhibited bulk superconductivity in terms of diamagnetic onset
below 50 K. The lower critical field (H
 c1) 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 FeO
 x
 impurity in the matrix. In specific heat measurements a jump is observed in
the vicinity of superconducting transition (T
 c
 ) 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 T
 c
 , 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.

Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50 K superconductor

Magnetization, x-ray diffraction, and specific-heat measurements reveal that SmCoAsO undergoes three magnetic phase transitions. A ferromagnetic transition attributed to the Co ions, emerges at ${T}_{C}=57\text{ }\text{K}$ with a small saturation moment of $\ensuremath{\sim}0.15\text{ }{\ensuremath{\mu}}_{B}/\text{Co}$. Reorientation of the Co moment to an antiferromagnetic state is obtained at ${T}_{N2}=45\text{ }\text{K}$. The relative high paramagnetic effective moment ${P}_{\text{eff}}=1.57\text{ }{\ensuremath{\mu}}_{B}/\text{Co}$ indicates an itinerant ferromagnetic state of the Co sublattice. The third magnetic transition at ${T}_{N1}=5\text{ }\text{K}$ is observed clearly in the specific-heat study only. Both magnetic and $^{57}\text{F}\text{e}$ Mossbauer studies show that substitution of small quantities of Fe for Co was unsuccessful.

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Anand Pal

Papers

Appearance of superconductivity in layered LaO0.5F0.5BiS2

Superconductivity and thermal properties of sulphur doped FeTe with effect of oxygen post annealing

Synthesis and physical properties of FeSe1/2Te1/2 superconductor

Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50 K superconductor

Magnetic phase transitions in SmCoAsO