Search

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) Å. 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. [ABSTRACT FROM AUTHOR]

Critical current densities (Jc) and irreversibility fields (Birr) of high-Tc superconductors AuBa2Can−1CunO2n+3 [Au-12(n−1)n, n=3,4] prepared under high pressure were determined from the hysteresis in DC magnetization loop. Both the Jc and Birr values of the Au-1234 phase were larger than those of Hg- and Bi-based cupurate superconductors, but smaller than those of the Y-123 superconductor. This result suggests that the electronic structure of Au-1234 is less anisotropic compared with the Hg- and Bi-phases. The Au-1223 phase showed very small Jc values corresponding to its small superconducting volume fraction. [Copyright &y& Elsevier]

Results of X-ray fluorescence measurements of MA[sub 2]Ca[sub n-1]Cu[sub n]O[sub 2n+3] compounds with [M-12(n 1)n] type structures, (C[sub 0.8]N[sub 0.2]Sr[sub 2]CuO[sub 5.3], [Cu[sub 0.25](C,N)[sub 0.75]]Sr[sub 2]CaCu[sub 2]O[sub y], Cu[sub 0.5]V[sub 0.5]Sr[sub 2]CaCu[sub 2]O[sub 7.5], Cu[sub 0.5]V[sub 0.5]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub 9.4], Cu[sub 0.5]V[sub 0.5]Sr[sub 2](Ca[sub 3.6]Sr[sub 0.4])Cu[sub 5]O[sub 13.5] and Cu[sub 0.5]V[sub 0.5]Sr[sub 2](Ca[sub 4.7]Sr[sub 0.3])Cu[sub 6]O[sub 15.3]), are presented. The experiments show that C-atoms form a distorted CO[sub 3] oxyacid group with a partial substitution of copper and nitrogen atoms in the M-sites. We conclude that the CO[sub 3, sup 2-] group in (C,N) Sr[sub 2]Ca[sub n-1]Cu[sub n]O[sub y] and (Cu,C,N) Sr[sub 2]Ca[sub n-1]Cu[sub n]O[sub y] is substituted by the NO[sub 2, sup -] which induces the creation of the hole carriers in these compounds. We have found that V-atoms in the given compounds form (VO[sub 4])[sup 3-] tetrahedrons and have a pentavalent state. [ABSTRACT FROM AUTHOR]

Abstract: The RuSr2RECu2O8 (RuRE-1212) and RuSr2RE1.5Ce0.5Cu2O10 (RuRE-1222; RE=rare earth) are the members of a class of material which exhibit both superconductivity and magnetic ordering. In this work high-pressure syntheses of the RE=Tb family and their magnetic properties are reported. They are tetragonal, RuTb-1212 belonging to P4/mmm space group, RuTb-1222 to I4/mmm. Compared to other ruthenocuprates, they show high magnetic ordering temperatures. This suggests that high magnetic moment of Tb influences the ordering of Ru moments in these compounds. [Copyright &y& Elsevier]

Additional charge carriers were introduced to the iron oxyarsenide Sr2ScFeAsO3 under a high-pressure condition, followed by measurements of electrical resistivity, the Hall coefficient, and magnetic susceptibility. The host compound Sr2ScFeAsO3 shows metallic conductivity down to ∼200 K and turns to show a semiconducting-like conductivity accompanied by a positive magnetoresistance (22% at 70 kOe). Although the carrier density is comparable at 300 K (5.9 × 1021 cm-3) with that of the other Fe-based superconductors, no superconductivity appears down to 2 K. This is primarily because the net carrier density decreases over three orders of magnitude on cooling and additionally a possible magnetic order at ∼120 K prevents carriers from pairing. The properties were altered largely by introducing the additional carriers. [ABSTRACT FROM AUTHOR]

Abstract: Detailed X-ray diffraction studies on RuSr2Eu1.5Ce0.5Cu2O10−δ (Eu–Ru-1222) magneto superconductor down to 13K at close temperature intervals revealed that with decreasing temperature, the c-parameter decreases linearly down to 100K, following the relation c =28.412(1)+2.5(1)×10−4 T and then becomes almost temperature independent on further lowering of temperature. Interestingly, the linear decrease in the a-parameter is seen only up to 180K. Below 180K, the observed values of the a-parameters are more than the value expected from the linear variation. This departure can be considered as development of strain in the system. Interestingly enough, these temperatures coincide with the complex magnetic ordering (T mag) of Ru in Ru-1222 system. This is the first report of the observation of the onset of excess volume and also of the strain along the a-axis near the magnetic ordering temperature in Ru-1222 superconductor, and indicates a coupling between the lattice and the magnetism in this system. Magnetization, magneto transport and thermoelectric power measurements being carried out on the same sample are also reported. The results of low temperature excess volume and the strain along a-axis of Ru-1222 compound are reportedly not seen in Ru-1212 (RuSr2GdCu2O8). [Copyright &y& Elsevier]

Abstract: We have studied the electronic structure near the Fermi level of the layered cobaltate superconductor Na0.35CoO2·1.3H2O using laser-excited ultrahigh-resolution photoemission spectroscopy (PES). In the normal state, we observed the formation of a pseudogap with an energy scale of ∼20meV. Across the superconducting transition, we observed the leading-edge shift at 3.5K compared to that at 10K, indicating superconducting gap (SC gap) opening having a gap value Δ of 0.5–0.7meV. The energy scale of the SC gap is ∼20 times smaller than that of the pseudogap, suggesting the existence of competing order parameters at low temperatures. [Copyright &y& Elsevier]

The local environment of fluorine atoms in Sr2Can – 1CunO2n + δF2 ± y(n=2,3) high-temperature superconductors (Tc = 99 and 111 K) is studied using soft x-ray emission and absorption spectroscopy. The fluorine spectra of the samples studied are found to be similar to those of SrF2, which supports the conjecture that fluorine atoms substitute for apex oxygen atoms and form double SrF layers. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

RuY1.5Ce0.5Sr2Cu2O10, is not superconducting (SC) and orders magnetically at TM=152 K. The Ru moment at 5 K is 0.75μB. Ferromagnetic hysteresis loops are observed below Tirr=100 K. At 100 K, the remanent magnetization (Mrem) and the coercive field (HC) become zero. Surprisingly, at Tirr a reappearance of antiferromagnetic (AFM) hysteresis loops are observed with a peak at 120 K for both Mrem and HC. The paramagnetic constants are: Peff=2.06μB (greater than the 1.73μB expected for low spin Ru5+) and θ=136 K which agrees well with TM. Substitution of Zn (2.5% atm.) for Cu in RuEu1.5Ce0.5 Sr2Cu2O10 (TC=38 K), suppresses TC but does not affect the magnetic features such as: TM and Tirr, Mrem and HC. This indicates that both SC and magnetic states are practically decoupled.We argue that the magnetic structure of this system becomes (i) AFM ordered at TM. (ii) Due to the tilting of the RuO6 octahedra away from the crystallographic c-axis, at Tirr, weak-ferromagnetic (W-FM) order is induced by the canting of the Ru moments. (iii) At TC (TM/TC∼4), the specific materials (M=Eu, Gd) become SC. Below TC, both SC and W-FM states coexist. [Copyright &y& Elsevier]

A new Au(Ba,La)2CuO5+δ (Au-1201) phase was synthesized at 6 GPa and 1250 °C. This compound is the first member of the Au-containing cuprate family. It crystallizes in an orthorhombic primitive cell with lattice parameters a=3.7976(3) A˚, b=3.8509(3) A˚, c=8.5749(9) A˚. Electron diffraction studies revealed the existence of additional weak reflections indicating a superlattice of as=5a, bs=b, cs=2c. A weak superconducting signal was observed below Tc=19 K in the magnetic susceptibility, but the diamagnetism was not large enough to assume bulk superconductivity. [Copyright &y& Elsevier]

Non-resonant V L2,3 and OKα X-ray emission spectra of a new series of (Cu,V)Sr2Can−1CunOy (n=3–7) superconductors are presented. We have found that oxygen atoms surround V-atoms in the given compounds, form a (VO4)3− tetrahedrons and have a pentavalent state. This induces holes due to the substitution of divalent copper by pentavalent vanadium ions providing a hole-doping mechanism of superconductivity in this series of compounds. A spectral estimation of the oxygen concentration shows that the oxygen content under high-pressure/high-temperature synthesis conditions is not changed considerably from the start to the final product. [Copyright &y& Elsevier]

Abstract: We report properties of the Zn-substituted polycrystalline superconductors BaFe1.87− x Zn x Co0.13As2 (x =0, 0.04, 0.06 and 0.08) prepared at ambient pressure condition. Electrical conductivity and magnetization measurements revealed that the superconductivity is suppressed by at most 2% substitution of Zn, which shows typical behavior of an anisotropically gaped superconductivity rather than an isotropically gaped superconductivity. With increasing the amount of Zn, weak change in superconductivity was observed. It is likely impossible to obtain BaFe1.87− x Zn x Co0.13As2 crystals with x >0.04 at ambient pressure condition. On the basis of the structural and the physical properties of the present system, we discuss a possible mechanism of the superconducting pairing. [Copyright &y& Elsevier]

Abstract: FeSr2EuCu2O8 (FeEu-1212) does not exhibit superconductivity when prepared by classical solid state route, because of iron atoms substitute partially copper atoms in the superconductive CuO2 planes. Recently, it has been found that high temperature annealing in Ar or N2 can favour the complete substitution of copper in CuO1−δ chains instead of in the CuO2 planes. After this annealing, the total oxygen content of the tetragonal FeSr2RECu2O8 decreases and the crystal structure changes to orthorhombic. It is possible to get superconductivity with a second annealing in O2 at low temperature. In this work a different approach was tried for first time. The samples of FeSr2EuCu2O8−δ series with δ =0, 0.5, 0.75 and 1 were prepared by high pressure high temperature (HPHT) synthesis starting from a mixture of Fe2O3, SrO2, Eu2O3, CuO and Cu. The final oxygen content was determined by the ratio between CuO and Cu. The structure of thus prepared samples changed from tetragonal for δ =0 to orthorhombic for δ =0.75 and 1. The iron atoms selectively occupy the CuO1−δ chains, if the oxygen content is low. Superconductive properties of these materials were studied, by subjecting them to high pressure and low temperature annealing with Ag2O2 or KClO4 as oxidizing agents. [Copyright &y& Elsevier]

The dynamics of the magnetic properties of polycrystalline RuSr2Ln1.5Ce0.5Cu2O10 (LnRu-1222, Ln=Gd, Y, Ho, Nd) have been studied by ac susceptibility. A frequency-dependent cusp was observed in χac vs. T measurements, which is interpreted as a spin-glass transition. These results are contrasted with the regular antiferromagnetic transition observed for YRu-1212. [Copyright &y& Elsevier]

Abstract: Oxygen vacant superconductors LaFeAsO1− δ were synthesized under a high-pressure condition. A bell-shaped feature in Tc vs. δ was observed for LaFeAsO1− δ as well as TbFeAsO1− δ . The optimized Tc was achieved at δ of 0.15, being comparable with that for TbFeAsO1− δ . The relatively wide δ window of LaFeAsO1− δ may merit scientific and technical studies of high-Tc superconductivity. [ABSTRACT FROM AUTHOR]

Abstract: We report on the result of muon spin relaxation measurements in a deuterated specimen of cobalt oxyhydrate superconductor, , which exhibits a hysteresis resembling ferromagnetic order in magnetic susceptibility. While the possibility of bulk ferromagnetic order is eliminated by the absence of spontaneous muon precession signal under zero field, the spectra indicate the appearance of magnetic domains below in accordance with a hysteresis in the susceptibility. This correlation demonstrates strong coupling between the water layers and the electronic state of CoO2 layers. [Copyright &y& Elsevier]