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- ItemDynamics of serrated flow in a bulk metallic glass(New York : American Institute of Physics, 2011) Ren, J.L.; Chen, C.; Wang, G.; Mattern, N.; Eckert, J.Under compression loading, bulk metallic glasses (BMGs) irreversibly deform through shear banding manifested as a serrated flow behavior. By using a statistical analysis together with a complementary dynamical analysis of the stress-time curves during serrated flow, we characterize the distinct spatiotemporal dynamical regimes and find that the plastic dynamic behavior of a Cu50Zr45Ti5 BMG changes from chaotic to self-organized critical behavior with increasing strain rate. This plastic dynamics transition with the strain rate is interpreted in the frame of the competence between the neighboring elastic strain field forming and relaxation processes.
- ItemPulsed laser deposition of thick BaHfO3-doped YBa 2Cu307-δ films on highly alloyed textured Ni-W tapes(Bristol : Institute of Physics Publishing, 2014) Sieger, M.; Hänisch, J.; Iida, K.; Gaitzsch, U.; Rodig, C.; Schultz, L.; Holzapfel, B.; Hühne, R.YBa2Cu3O7-δ (YBCO) films with a thickness of up to 3 μm containing nano-sized BaHfO3 (BHO) have been grown on Y2O3/Y-stabilized ZrO2/CeO 2 buffered Ni-9at% W tapes by pulsed laser deposition (PLD). Structural characterization by means of X-ray diffraction confirmed that the YBCO layer grew epitaxial. A superconducting transition temperature T c of about 89 K with a transition width of 1 K was determined, decreasing with increasing BHO content. Critical current density in self-field and at 0.3 T increased with increasing dopant level.
- ItemMagnetic flux-trapping of anisotropic-grown Y-Ba-Cu-O bulk superconductors during and after pulsed-field magnetizing processes(Milton Park : Taylor & Francis, 2014) Oka, T.; Yamada, Y.; Horiuchi, T.; Ogawa, J.; Fukui, S.; Sato, T.; Yokoyama, K.; Langer, M.The magnetic flux penetration into the melt-textured Y-Ba-Cu-O high temperature superconducting bulk magnets were precisely evaluated during and after the pulsed field magnetization processes operated at 30 K. The bulk magnets were carefully fabricated by the cold seeding method with use of a single and a pair of seed crystals composed of the Nd-Ba-Cu-O thin films. These seed crystals were put on the top surfaces of the precursors to let the large grains grow during the heat treatments. We observed the flux penetrations which occurred in the lower applied-field regions at around 3.1 T for the samples bearing the twin seeds than those of the single-seeded crystals at around 3.8 T. This means that the magnetic fluxes are capable of invading into the twin-seeded samples more easily than the single-seeds. It suggests that the anisotropic grain growths of parallel and normal to the rows of seed crystals affects the variations of Jc values with different distributions of the pinning centers, results in the preferential paths for the invading magnetic fluxes.
- ItemCombinatorial synthesis of (YxGd1-x)Ba2Cu3Ox superconducting thin films(Amsterdam [u.a.] : Elsevier, 2012) Kirchner, A.; Erbe, M.; Freudenberg, T.; Hühne, R.; Feys, J.; Van Driessche, I.; Schultz, L.; Holzapfel, B.Environmentally friendly water-based YBa2Cu3Ox (YBCO) and GdBa2Cu3Ox (GdBCO) precursor solutions were synthesized to realize thin films by chemical solution deposition. Pure YBCO and GdBCO precursor solutions were used for ink plotting on SrTiO3 substrates and subsequent thermal treatment at the corresponding crystallization temperature. Phase formation of Gd123 requires a higher crystallization temperature of 840 °C compared to the Y123 phase. The critical temperature of YBCO films is about 92 K with a sharp transition into the superconducting state. Micro liter sized ink volumes of YBCO and GdBCO were successfully mixed for two-dimensional ink plotting of a (YxGd1-x)Ba2Cu3Ox film library. A homogeneous surface and no indication of a-axis growth were found in all mixed films.
- ItemThe Bain library: A Cu-Au buffer template for a continuous variation of lattice parameters in epitaxial films(New York : American Institute of Physics, 2014) Kauffmann-Weiss, S.; Hamann, S.; Reichel, L.; Siegel, A.; Alexandrakis, V.; Heller, R.; Schultz, L.; Ludwig, A.; Fähler, S.Smallest variations of the lattice parameter result in significant changes in material properties. Whereas in bulk, lattice parameters can only be changed by composition or temperature, coherent epitaxial growth of thin films on single crystals allows adjusting the lattice parameters independently. Up to now only discrete values were accessible by using different buffer or substrate materials. We realize a lateral variation of in-plane lattice parameters using combinatorial film deposition of epitaxial Cu-Au on a 4-in. Si wafer. This template gives the possibility to adjust the in-plane lattice parameter over a wide range from 0.365 nm up to 0.382 nm.
- ItemStructural evolution in Ti-Cu-Ni metallic glasses during heating(New York : American Institute of Physics, 2015) Gargarella, P.; Pauly, S.; Stoica, M.; Vaughan, G.; Afonso, C.R.M.; Kühn, U.; Eckert, J.The structural evolution of Ti50Cu43Ni7 and Ti55Cu35Ni10 metallic glasses during heating was investigated by in-situ synchrotron X-ray diffraction. The width of the most intense diffraction maximum of the glassy phase decreases slightly during relaxation below the glass transition temperature. Significant structural changes only occur above the glass transition manifesting in a change in the respective peak positions. At even higher temperatures, nanocrystals of the shape memory B2-Ti(Cu,Ni) phase precipitate, and their small size hampers the occurrence of a martensitic transformation.
- ItemSuperconducting switching due to a triplet component in the Pb/Cu/Ni/Cu/Co2Cr1-xFexAly spin-valve structure(Frankfurt am Main : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2019) Kamashev, A.A.; Garif'yanov, N.N.; Validov, A.A.; Schumann, J.; Kataev, V.; Büchner, B.; Fominov, Y.V.; Garifullin, I.A.We report the superconducting properties of the Co2Cr1-xFexAly/Cu/Ni/Cu/Pb spin-valve structure the magnetic part of which comprises the Heusler alloy layer HA = Co2Cr1-xFexAly with a high degree of spin polarization (DSP) of the conduction band and a Ni layer of variable thickness. The separation between the superconducting transition curves measured for the parallel (α = 0°) and perpendicular (α = 90°) orientation of the magnetization of the HA and the Ni layers reaches up to 0.5 K (α is the angle between the magnetization of two ferromagnetic layers). For all studied samples the dependence of the superconducting transition temperature Tc on α demonstrates a deep minimum in the vicinity of the perpendicular configuration of the magnetizations. This suggests that the observed minimum and the corresponding full switching effect of the spin valve is caused by the long-range triplet component of the superconducting condensate in the multilayer. Such a large effect can be attributed to a half-metallic nature of the HA layer, which in the orthogonal configuration efficiently draws off the spin-polarized Cooper pairs from the space between the HA and Ni layers. Our results indicate a significant potential of the concept of a superconducting spin-valve multilayer comprising a half-metallic ferromagnet, recently proposed by A. Singh et al., Phys. Rev. X 2015, 5, 021019, in achieving large values of the switching effect.
- ItemHigh-field ESR studies of the quantum spin magnet CaCu2O 3(Milton Park : Taylor & Francis, 2006) Goiran, M.; Costes, M.; Broto, J.M.; Chou, F.C.; Klingeler, R.; Arushanov, E.; Drechsler, S.-L.; Büchner, B.; Kataev, V.We report an electron spin resonance (ESR) study of the s = 1/2 Heisenberg pseudo-ladder magnet CaCu2O3 in pulsed magnetic fields up to 40 T. At sub-terahertz frequencies we observe an ESR signal originating from a small amount of uncompensated spins residing presumably at the imperfections of the strongly antiferromagnetically correlated host spin lattice. The data give evidence that these few per cent of 'extra' spin states are coupled strongly to the bulk spins and are involved in the antiferromagnetic (AF) ordering at TN = 25 K. By mapping the frequency/resonance field diagram we have determined a small gap for magnetic excitations below TN of the order of ~0.3–0.8 meV. Such a small value of the gap explains the occurrence of the spin-flop transition in CaCu2O3 at weak magnetic fields μ0Hsf ~ 3 T. Qualitative changes of the ESR response with the increasing field strength give indications that strong magnetic fields reduce the AF correlations and may even suppress the long-range magnetic order in CaCu2O3. ESR data support scenarios with a significant role of the 'extra' spin states for the properties of low-dimensional quantum magnets.
- ItemFermi surface nesting in several transition metal dichalcogenides(Milton Park : Taylor & Francis, 2008) Inosov, D.S.; Zabolotnyy, V.B.; Evtushinsky, D.V.; Kordyuk, A.A.; Büchner, B.; Follath, R.; Berger, H.; Borisenko, S.V.By means of high-resolution angle-resolved photoelectron spectroscopy (ARPES), we have studied the fermiology of 2H transition metal dichalcogenide polytypes TaSe2, NbSe2 and Cu0.2NbS 2. The tight-binding model of the electronic structure, extracted from ARPES spectra for all three compounds, was used to calculate the Lindhard function (bare spin susceptibility), which reflects the propensity to charge density wave (CDW) instabilities observed in TaSe2 and NbSe 2. We show that though the Fermi surfaces of all three compounds possess an incommensurate nesting vector in the close vicinity of the CDW wave vector, the nesting and ordering wave vectors do not exactly coincide, and there is no direct relationship between the magnitude of the susceptibility at the nesting vector and the CDW transition temperature. The nesting vector persists across the incommensurate CDW transition in TaSe2 as a function of temperature despite the observable variations of the Fermi surface geometry in this temperature range. In Cu0.2NbS2, the nesting vector is present despite different doping levels, which leads us to expect a possible enhancement of the CDW instability with Cu intercalation in the Cu xNbS2 family of materials.