Doping effects of Co, Ni, and Cu in FeTe0.65Se0.35 single crystals

The resistivity, magnetoresistance, and magnetic susceptibility are measured in single crystals of FeTe0.65Se0.35 with Cu, Ni, and Co substitutions for Fe. The crystals are grown by Bridgman's method. The resistivity measurements show that superconductivity disappears with the rate which correlates with the nominal valence of the impurity. From magnetoresistance we evaluate doping effect on the basic superconducting parameters, such as upper critical field and coherence length. We find indications that doping leads to two component superconducting behavior, possibly because of local charge depression around impurities.Comment: 4 pages, 4 figures, 1 table, Proceedings of the XV-th National School "Hundred Years of Superconductivity", Kazimierz Dolny, October 9-13, 201

Localization and Interaction Effects in Strongly Underdoped La2-xSrxCuO4

The in-plane magnetoresistance (MR) in La2-xSrxCuO4 films with 0.03 < x < 0.05 has been studied in the temperature range 1.6 K to 100 K, and in magnetic fields up to 14 T, parallel and perpendicular to the CuO2 planes. The behavior of the MR is consistent with a predominant influence of interaction effects at high temperatures, switching gradually to a regime dominated by spin scattering at low T. Weak localization effects are absent. A positive orbital MR appears close to the boundary between the antiferromagnetic and the spin-glass phase, suggesting the onset of Maki-Thompson superconducting fluctuations deep inside the insulating phase.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Letter

Three terminal capacitance technique for magnetostriction and thermal expansion measurements

An instrument has been constructed to measure a large range of magnetostriction and thermal expansion between room temperature and 4 K in a superconductive split-coil magnet, that allows investigation in magnetic fields up to 12 T. The very small bulk samples (up to 1 mm in size) as well as big ones (up to 13 mm) of the irregular form can be measured. The possibility of magnetostriction investigation in thin films is shown. A general account is given of both electrical and the mechanical aspects of the design of capacitance cell and their associated electronic circuitry. A simple lever device is proposed to increase the sensitivity twice. The resulting obtained sensitivity can be 0.5 Angstrom. The performance of the technique is illustrated by some preliminary measurements of the magnetostriction of superconducting MgB2, thermal expansion of (La0.8Ba0.2)0.93MnO3 single crystal and magnetoelastic behavior of the Ni/Si(111) and La0.7Sr0.3CoO3/SAT0.7CAT0.1LA0.2(001) cantilevers.Comment: 6 pages, 6 figures, journal pape

BaWO4:Ce Single Crystals Codoped with Na Ions

Single crystals of BaWO4, BaWO4:0.5at.%Ce; BaWO4:1at.%Ce; BaWO4:0.5at.%Ce,1at.%Na; and BaWO4:1at.%Ce,2at.%Na were grown from an inductively heated iridium crucible by the Czochralski method on a Malvern MSR4 puller. They were investigated using Electron Paramagnetic Resonance (EPR) spectroscopy at helium temperatures. One isolated center of high (D2d or S4) symmetry was found and two or more other centers of lower symmetry were identified, depending on crystal doping. From the fitting using the EPR-NMR program, the following parameters of g-matrix for the high symmetry center were found: gx = 1.505, gy = 1.505, and gz = 2.731. The linewidth vs. temperature revealed an increasing exponential tendency with increasing temperature. It showed one phonon at the lower temperatures and a Raman + Orbach effect at the higher temperatures. Radioluminescence and pulse height spectra showed rather poor scintillation properties, without any contribution from cerium emission

Reinforced Concrete Floors in Historic Buildings from the Beginning and the Middle of the 20th Century - Examples of Structural Strengthening in the Process of Revitalization

The paper presents a historical outline of structural solutions of reinforced concrete floors from the turn of the 19th and 20th centuries to the half of the 20th century in the Lower Silesia region of Poland. It is based on the analysis of archival documentation and expert research carried out during the design of the revitalization of historic public and industrial buildings. The structural typology of some simple RC floors slabs used in that time of introduction of concrete into construction life as well as constructional solutions of buildings erected in western Poland in those days are presented. Nowadays, while some of these buildings undergo refurbishment process to adapt them to new functional aims these RC floors have to be strengthened using different methods, depending on the assessment results. In some of the presented design study cases assessed technical state and load bearing capacity of floors ensure the possibility of their further use without the need for significant reinforcements, except for the need for surface material repairs. However, in some cases due to concrete deterioration processes and loss of its durability, despite necessity of material renovation, structural strengthening methods needed to be applied. For example, increasing the load bearing capacity of floors by making additional concrete layers cooperating with the existing reinforced concrete slab or by changing the static scheme by making new supports up to the complete replacement of floors (not only concrete ones) with modern, concrete rib-andbeam or composite ones were considered

Growth conditions, structure, and superconductivity of pure and metal-doped FeTe1-xSex single crystals

Superconducting single crystals of pure FeTe1 xSex and FeTe0.65Se0.35 doped with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd into Fe ions site have been grown applying Bridgman's method. It has been found that the sharpness of transition to the superconducting state in FeTe1 xSex is evidently inversely correlated with crystallographic quality of the crystals. Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in FeTe0.65Se0.35 crystals. The remaining examined ions do not incorporate into the crystal structure. Nevertheless, they form inclusions together with selenium, tellurium and/or iron, what changes the chemical composition of host matrix and therefore influences Tc value. Small disorder introduced into magnetic sublattice, by partial replacement of Fe ions by slight amount of nonmagnetic ions of Cu (~ 1.5 at%) or by magnetic ions of Ni (~ 2 at%) and Co (~5 at%) with spin value different than that of Fe ion, completely suppresses superconductivity in FeTe1 xSex system. This indicates that even if superconductivity is observed in the system containing magnetic ions it can not survive when the disorder in magnetic ions sublattice is introduced, most likely because of magnetic scattering of Cooper pairs.Comment: 18 pages, 12 figures, 3 table

Impurity and strain effects on the magnetotransport of La1.85Sr0.15Cu(1-y)Zn(y)O4 films

The influence of zinc doping and strain related effects on the normal state transport properties(the resistivity, the Hall angle and the orbital magneto- resistance(OMR) is studied in a series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with values of y between 0 and 0.12 and various degrees of strain induced by the mismatch between the films and the substrate. The zinc doping affects only the constant term in the temperature dependence of cotangent theta but the strain affects both the slope and the constant term, while their ratio remains constant.OMR is decreased by zinc doping but is unaffected by strain. The ratio delta rho/(rho*tan^2 theta) is T-independent but decreases with impurity doping. These results put strong constraints on theories of the normal state of high- temperature superconductors