Reentrant superconductivity in superconductor/ferromagnetic-alloy bilayers

We studied the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state establishing due to the proximity effect in superconducting Nb/Cu41Ni59 bilayers. Using a special wedge-type deposition technique, series of 20-35 samples could be fabricated by magnetron sputtering during one run. The layer thickness of only a few nanometers, the composition of the alloy, and the quality of interfaces were controlled by Rutherford backscattering spectrometry, high resolution transmission electron microscopy, and Auger spectroscopy. The magnetic properties of the ferromagnetic alloy layer were characterized with superconducting quantum interference device (SQUID) magnetometry. These studies yield precise information about the thickness, and demonstrate the homogeneity of the alloy composition and magnetic properties along the sample series. The dependencies of the critical temperature on the Nb and Cu41Ni59 layer thickness, Tc(dS) and Tc(dF), were investigated for constant thickness dF of the magnetic alloy layer and dS of the superconducting layer, respectively. All types of non-monotonic behaviors of Tc versus dF predicted by the theory could be realized experimentally: from reentrant superconducting behavior with a broad extinction region to a slight suppression of superconductivity with a shallow minimum. Even a double extinction of superconductivity was observed, giving evidence for the multiple reentrant behavior predicted by theory. All critical temperature curves were fitted with suitable sets of parameters. Then, Tc(dF) diagrams of a hypothetical F/S/F spin-switch core structure were calculated using these parameters. Finally, superconducting spin-switch fabrication issues are discussed in detail in view of the achieved results.Comment: 34 pages, 9 figure

Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations

A comprehensive study of the electronic properties of monoclinic MoO2 from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations. For the latter, the new full-potential augmented spherical wave (ASW) method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional hole-like surfaces centered around the Z- and B-point could be resolved; these surfaces were an artefact of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of MoO2 and the neighbouring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of VO2 and NbO2, which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.Comment: 17 pages, 21 figures, more information at http://www.physik.uni-augsburg.de/~eyert

Reentrant superconductivity in superconductor/ferromagnetic-alloy bilayers

We studied the Fulde-Ferrell-Larkin-Ovchinnikov-type state established due to the proximity effect in superconducting Nb/ Cu41 Ni59 bilayers. Using a special wedge-type deposition technique, series of 20-35 samples could be fabricated by magnetron sputtering during one run. The layer thickness of only a few nanometers, the composition of the alloy, and the quality of interfaces were controlled by Rutherford backscattering spectrometry, high-resolution transmission electron microscopy, and Auger spectroscopy. The magnetic properties of the ferromagnetic alloy layer were characterized with superconducting quantum interference device magnetometry. These studies yield precise information about the thickness and demonstrate the homogeneity of the alloy composition and magnetic properties along the sample series. The dependencies of the critical temperature on the Nb and Cu41 Ni 59 layer thickness, Tc (dS) and Tc (dF), were investigated for constant thickness dF of the magnetic alloy layer and dS of the superconducting layer, respectively. All types of nonmonotonic behaviors of Tc versus d F predicted by the theory could be realized experimentally, from reentrant superconducting behavior with a broad extinction region to a slight suppression of superconductivity with a shallow minimum. Even a double extinction of superconductivity was observed, giving evidence for the multiple reentrant behavior predicted by theory. All critical temperature curves were fitted with suitable sets of parameters. Then, Tc (dF) diagrams of a hypothetical ferromagnet/superconductor/ferromagnet spin-switch core structure were calculated using these parameters. Finally, superconducting spin-switch fabrication issues are discussed in detail in view of the achieved results. © 2010 The American Physical Society

The Influence of the Track Axis Curvature at Railway Filler-Beam Deck Bridges

The article presents a comparative study between the simplified method calculation proposed by the prescriptions of design codes and the analysis with the FEM program LUSAS [1], regarding the influence of the curvature of the track axis at railway bridges with steel beams embedded in concrete

Reentrant superconductivity in superconductor/ferromagnetic-alloy bilayers

We studied the Fulde-Ferrell-Larkin-Ovchinnikov-type state established due to the proximity effect in superconducting Nb/ Cu41 Ni59 bilayers. Using a special wedge-type deposition technique, series of 20-35 samples could be fabricated by magnetron sputtering during one run. The layer thickness of only a few nanometers, the composition of the alloy, and the quality of interfaces were controlled by Rutherford backscattering spectrometry, high-resolution transmission electron microscopy, and Auger spectroscopy. The magnetic properties of the ferromagnetic alloy layer were characterized with superconducting quantum interference device magnetometry. These studies yield precise information about the thickness and demonstrate the homogeneity of the alloy composition and magnetic properties along the sample series. The dependencies of the critical temperature on the Nb and Cu41 Ni 59 layer thickness, Tc (dS) and Tc (dF), were investigated for constant thickness dF of the magnetic alloy layer and dS of the superconducting layer, respectively. All types of nonmonotonic behaviors of Tc versus d F predicted by the theory could be realized experimentally, from reentrant superconducting behavior with a broad extinction region to a slight suppression of superconductivity with a shallow minimum. Even a double extinction of superconductivity was observed, giving evidence for the multiple reentrant behavior predicted by theory. All critical temperature curves were fitted with suitable sets of parameters. Then, Tc (dF) diagrams of a hypothetical ferromagnet/superconductor/ferromagnet spin-switch core structure were calculated using these parameters. Finally, superconducting spin-switch fabrication issues are discussed in detail in view of the achieved results. © 2010 The American Physical Society

Reentrant superconductivity in superconductor/ferromagnetic-alloy bilayers

We studied the Fulde-Ferrell-Larkin-Ovchinnikov-type state established due to the proximity effect in superconducting Nb/ Cu41 Ni59 bilayers. Using a special wedge-type deposition technique, series of 20-35 samples could be fabricated by magnetron sputtering during one run. The layer thickness of only a few nanometers, the composition of the alloy, and the quality of interfaces were controlled by Rutherford backscattering spectrometry, high-resolution transmission electron microscopy, and Auger spectroscopy. The magnetic properties of the ferromagnetic alloy layer were characterized with superconducting quantum interference device magnetometry. These studies yield precise information about the thickness and demonstrate the homogeneity of the alloy composition and magnetic properties along the sample series. The dependencies of the critical temperature on the Nb and Cu41 Ni 59 layer thickness, Tc (dS) and Tc (dF), were investigated for constant thickness dF of the magnetic alloy layer and dS of the superconducting layer, respectively. All types of nonmonotonic behaviors of Tc versus d F predicted by the theory could be realized experimentally, from reentrant superconducting behavior with a broad extinction region to a slight suppression of superconductivity with a shallow minimum. Even a double extinction of superconductivity was observed, giving evidence for the multiple reentrant behavior predicted by theory. All critical temperature curves were fitted with suitable sets of parameters. Then, Tc (dF) diagrams of a hypothetical ferromagnet/superconductor/ferromagnet spin-switch core structure were calculated using these parameters. Finally, superconducting spin-switch fabrication issues are discussed in detail in view of the achieved results. © 2010 The American Physical Society