R. Tidecks

Karlsruhe Institute of Technology, Carlsruhe, Baden-Württemberg, Germany

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Publications (95)192.76 Total impact

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    ABSTRACT: We fabricated a nanolayered hybrid superconductor-ferromagnet spin-valve structure, the resistive state of which depends on the preceding magnetic field polarity. The effect is based on a strong exchange bias (about -2 kOe) on a diluted ferromagnetic copper-nickel alloy and generation of a long range odd in frequency triplet pairing component. The difference of high and low resistance states at zero magnetic field is 90% of the normal state resistance for a transport current of 250 {\mu}A and still around 42% for 10 {\mu}A. Both logic states of the structure do not require biasing fields or currents in the idle mode.
    Applied Physics Letters 08/2013; 103(6):062604. · 3.79 Impact Factor
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    ABSTRACT: Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers constitute the core of a superconducting spin valve. The switching effect of the spin valve is based on interference phenomena occurring due to the proximity effect at the S/F interfaces. A remarkable effect is only expected if the core structure exhibits strong critical temperature oscillations, or most favorable, reentrant superconductivity, when the thickness of the ferromagnetic layer is increased. The core structure has to be grown on an antiferromagnetic oxide layer (or such layer to be placed on top) to pin by exchange bias the magnetization-orientation of one of the ferromagnetic layers. In the present paper we demonstrate that this is possible, keeping the superconducting behavior of the core structure undisturbed.
    Journal of Applied Physics 07/2013; 114(3):033903 - 033903-8. · 2.21 Impact Factor
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    ABSTRACT: The theory of superconductor-ferromagnet (S-F) heterostructures with two ferromagnetic layers predicts the generation of a long-range, odd-in-frequency triplet pairing at non-collinear alignment (NCA) of the magnetizations of the F-layers. This triplet pairing has been detected in a Nb/Cu41Ni59/nc-Nb/Co/CoOx spin-valve type proximity effect heterostructure, in which a very thin Nb film between the F-layers serves as a normal conducting (nc) spacer. The resistance of the sample as a function of an external magnetic field shows that for not too high fields the system is superconducting at a collinear alignment of the Cu41Ni59 and Co layer magnetic moments, but switches to the normal conducting state at a NCA configuration. This indicates that the superconducting transition temperature Tc for NCA is lower than the fixed measuring temperature. The existence of a minimum Tc, at the NCA regime below that one for parallel or antiparallel alignments of the F-layer magnetic moments, is consistent with the theoretical prediction of a singlet superconductivity suppression by the long-range triplet pairing generation.
    Physical Review B 04/2013; 87(14):144507. · 3.77 Impact Factor
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    ABSTRACT: A surface acoustic wave (SAW) delay line is used to study the metal-to-insulator (MI) transition of V2O3 thin films deposited on a piezoelectric LiNbO3 substrate. Effects contributing to the sound velocity shift of the SAW which are caused by elastic properties of the lattice of the V2O3 films when changing the temperature are separated from those originating from the electrical conductivity. For this purpose the electric field accompanying the elastic wave of the SAW has been shielded by growing the V2O3 film on a thin metallic Cr interlayer (coated with Cr2O3), covering the piezoelectric substrate. Thus, the recently discovered lattice precursor of the MI transition can be directly observed in the experiments, and its fine structure can be investigated.
    Applied Physics Letters 03/2013; 102(10). · 3.79 Impact Factor
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    ABSTRACT: The upper critical magnetic field H_{c2} in thin-film FSF trilayer spin-valve cores is studied experimentally and theoretically in geometries perpendicular and parallel to the heterostructure surface. The series of samples with variable thicknesses of the bottom and of the top Cu_{41}Ni_{59} F-layers are prepared in a single run, utilizing a wedge deposition technique. The critical field H_{c2} is measured in the temperature range $0.4-8$ K and for magnetic fields up to 9 Tesla. A transition from oscillatory to reentrant behavior of the superconducting transition temperature versus F-layers thickness, induced by an external magnetic field, has been observed for the first time. In order to properly interpret the experimental data, we develop a quasiclassical theory, enabling one to evaluate the temperature dependence of the critical field and the superconducting transition temperature for an arbitrary set of the system parameters. A fairly good agreement between our experimental data and theoretical predictions is demonstrated for all samples, using a single set of fit parameters. This confirms adequacy of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) physics in determining the unusual superconducting properties of the studied Cu_{41}Ni_{59}/Nb/Cu_{41}Ni_{59} spin-valve core trilayers.
    Superconductor Science and Technology 02/2013; 26(8):085003. · 2.76 Impact Factor
  • Chemical Vapor Deposition 01/2013; 19:15. · 1.32 Impact Factor
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    ABSTRACT: Interference effects of the superconducting pairing wave function in thin film bilayers of Nb as a superconductor (S) and Cu41Ni59 as ferromagnetic (F) material lead to critical temperature oscillations and reentrant superconductivity for increasing F-layer thickness. The phenomenon is generated by the Fulde-Ferrell Larkin-Ovchinnikov (FFLO) like state establishing in these geometries. So far detailed investigations were performed on S/F bilayers. Recently, we could also realize the phenomena in F/S bilayers where the S-metal now is grown on top of the F-material. Combining both building blocks yields an F/S/F trilayer, representing the core structure of the superconducting spin valve. Also for this geometry we observed deep critical temperature oscillations and reentrant superconductivity, which is the basis to obtain a large spin switching effect, i.e. a large shift in the critical temperature, if the relative orientation of the magnetizations of the F-layers is changed from parallel to antiparallel.
    Journal of Physics Conference Series 12/2012; 400(2):022143.
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    ABSTRACT: Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers, in which the establishing of a Fulde-Ferrell Larkin-Ovchinnikov (FFLO) like state leads to interference effects of the superconducting pairing wave function, form the core of the superconducting spin valve. The realization of strong critical temperature oscillations in such trilayers, as a function of the ferromagnetic layer thicknesses or, even more efficient, reentrant superconductivity, are the key condition to obtain a large spin valve effect, i.e. a large shift in the critical temperature. Both phenomena have been realized experimentally in the Cu 41 Ni 59 /Nb/Cu 41 Ni 59 trilayers investigated in the present work.
    Annalen der Physik 01/2012; 524(1):37. · 1.51 Impact Factor
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    ABSTRACT: The theoretical description of the Fulde-Ferrell-Larkin-Ovchinnikov like state establishing in nanostructered bilayers of ferromagnetic (F) and superconducting (S) material leads to critical temperature oscillations and reentrant superconductivity as the F-layer thickness gradually increases. The experimental realization of these phenomena is an important prerequisite for the fabrication of the Ferromagnet/Superconductor/Ferromagnet core structure of the superconducting spin-valve. A switching of the spin-valve is only expected if such non-monotonic critical temperature behavior is observed in F/S bilayers as well as in the S/F bilayers, a combination of which the spin-valve core structure can be regarded to consist of. In our former investigations we could demonstrate the required non-monotonic behavior of the critical temperature in S/F bilayers. In this study we succeeded in the preparation of F/S bilayers, where the superconducting material is now grown on top of the ferromagnetic metal, which show deep critical temperature oscillations as a function of the ferromagnetic layer thickness as well as an extinction and recovery, i.e. a reentrant behavior, of superconductivity. Especially, the latter is necessary to obtain a spin-valve with a large critical temperature shift between the parallel and antiparallel configurations of magnetizations in the F layers.
    Superconductor Science and Technology 09/2011; 24(9):095004. · 2.76 Impact Factor
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    ABSTRACT: 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.
    Physical Review B 08/2010; 82(5):054517. · 3.77 Impact Factor
  • ChemInform 01/2010; 30(51).
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    ABSTRACT: In a ferromagnet (F) being in contact with a superconductor (S) an unconventional finite-momentum pairing of electrons forming Cooper pairs occurs. As a consequence, interference effects of the pairing wave function, leading to an oscillation of the critical temperature for increasing F-layer thickness in S/F bilayers, including extinction and recovery of the superconducting state, were predicted by theory. We observed experimentally all types of this behavior, calculated theoretically, in Nb/Cu1 − x Ni x bilayers (x = 0.59) of nanometer film thickness, prepared by magnetron sputtering (utilizing a moving magnetron deposition technique to provide a superb homogeneity of the ultrathin Nb layers), including a double extinction of superconductivity, giving evidence for a multiple reentrant state.
    JETP Letters 09/2009; 90(2):139-142. · 1.52 Impact Factor
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    ABSTRACT: A dimensional crossover of superconducting fluctuations in an external magnetic field, applied parallel to the layers, has been found for superconductor/ferromagnet bilayers of Nb/Cu(41)Ni(59). By lowering the temperature, a reduction of the superconducting nuclei size occurs. As soon as the size of the nuclei becomes smaller than the thickness of the superconducting bilayer structure, the dimensionality changes. The temperature dependence of the fluctuation conductivity exhibits a 2D behaviour in zero and weak magnetic fields in the vicinity of the critical temperature, switching to a 3D behaviour in a strong magnetic field at low temperatures.
    Journal of Physics Condensed Matter 06/2009; 21(25):254202. · 2.36 Impact Factor
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    ABSTRACT: We report on the first observation of a double suppression of superconductivity in a superconductor/ferromagnet layered system. The result was obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu41Ni59 with dNb ≊ 6.2 nm. As the thickness of the ferromagnetic alloy gradually increases, the superconducting transition temperature Tc drops sharply until a complete suppression of superconductivity is observed at dcuNi ≊ 2.5 nm. At further increase of the Cu41Ni59 layer thickness, superconductivity restores at dcuNi ≊ 24 nm. Then, with a subsequent increase of dcuNi, superconductivity vanishes again at dcuNi ≊ 38 nm. Our experiments give evidence for the realization of the quasi-one dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic alloy layer.
    Journal of Physics Conference Series 03/2009; 150(5):052242.
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    ABSTRACT: In superconductor–ferromagnet (S/F) metallic contacts, the superconducting condensate penetrates through the S/F interface into a ferromagnetic layer. In contrast to the conventional S/N proximity effect, the pairing wave function not only decays deep into the F metal, but simultaneously oscillates. Interference of the oscillating pairing function in a ferromagnetic film gives rise to a modulation of the pairing function flux crossing the S/F interface, which results in oscillations of superconducting transition temperature of the adjacent S layer. In this work, we report on the experimental observation of the superconductivity reentrance phenomenon with double suppression of the superconductivity in Nb ∕ Cu1 − x Ni x bilayers as a function of the ferromagnetic layer thickness, d CuNi. The superconducting T c drops sharply with increasing d CuNi till total suppression of superconductivity at d CuNi ≈ 2. 5 nm. At a further increase of the Nb ∕ Cu1 − x Ni x layer thickness, the superconductivity restores at d CuNi ≥ 24 nm. Then, with the subsequent increase of d CuNi, the superconductivity vanishes again at d CuNi ≈ 38 nm.
    12/2008: pages 3-11;
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    ABSTRACT: The propagation of the first ionization wave in a compact fluorescent lamp (T4 tube with standard electrodes) during ignition was investigated for various initial dc-voltages (both polarities measured against ground) and gas compositions (with and without mercury). In addition the effect of the presence of a fluorescent powder coating was studied. The propagation velocity of the initial wave was measured by an assembly of photomultipliers installed along the tube, which detected the light emitted by the wave head. The propagation was found to be faster for positive than for negative polarity. This effect is explained involving processes in the electrode region as well as in the wave head. Waves propagate faster in the presence of a fluorescent powder coating than without it and gases of lighter mass show a faster propagation than gases with higher mass.
    Journal of Physics D Applied Physics 07/2008; 41(14):144011. · 2.53 Impact Factor
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    ABSTRACT: The metal-to-insulator (MI) transition of a V2O3 thin film is studied, using a surface acoustic wave delay line. The V2O3 film covers not only the sound path but also one of the interdigital transducers (IDTs). The resulting mismatch of the IDTs detunes the delay line, until the film passes through the MI transition. This “self-retuning” behavior makes the device extremely sensitive to the initial changes of the electrical and dielectric properties of the film during the MI transition. Attenuation and sound velocity are measured between 260 and 4.2 K. Both suggest a precursor to the MI transition in the paramagnetic metallic regime. The existence of a precursor is consistent with recent extended x-ray absorption fine structure measurements. An oscillatory behavior with steep reductions of the sound velocity is observed during the MI transition. The reductions of the sound velocity probably indicate the recently predicted anomaly at the Mott transition.
    Journal of Applied Physics 03/2008; 103(6):063705-063705-7. · 2.21 Impact Factor
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    ABSTRACT: Oscillating behavior of superconductivity in ultrathin bilayers of niobium and ferromagnetic alloy Cu41Ni59 has been observed. This phenomenon was most pronounced at a Nb layer thickness of about 7.3 nm: the superconducting transition temperature T c first sharply decreased with an increase in the ferromagnetic alloy thickness to complete suppression of superconductivity at the ferromagnetic alloy thickness d CuNi ≈ 4 nm. With a further increase in the thickness d CuNi, the superconductivity was restored at d CuNi ≥ 13 nm. This strongly nonmonotonic and reentrant behavior of superconductivity in Nb/Cu41Ni59 bilayers is attributed to implementation of a state in the ferromagnetic alloy that is similar to the quasi-one-dimensional Fulde-Ferrell-Larkin-Ovchinnikov state.
    Bulletin of the Russian Academy of Sciences Physics 01/2008; 72(2):144-147.
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    ABSTRACT: Starting with an introduction to surface acoustic waves, their generation and detection using interdigital transducers (IDTs) on piezoelectric materials (e.g. LiNbO3 and ZnO) will be reviewed. Then the application of surface acoustic waves in electronic devices will be presented. Moreover, recent studies, using the technique of attaching the material of investigation onto the sound path of the acoustic delay line between the IDTs is discussed.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    Proc SPIE 02/2007;
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    ABSTRACT: According to the crystal structure of MgB2 and band structure calculations quasi–two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical fields and resistance measurements of 30 nm thick MgB2 films grown on MgO single crystalline substrate. A linear temperature dependence of the parallel and perpendicular upper critical fields indicates a 3D-like penetration of magnetic field into the sample. Resistivity measurements, in contrast, yield a temperature dependence of fluctuation conductivity above Tc which agrees with the Aslamazov-Larkin theory of fluctuations in 2D superconductors. We consider this finding as an experimental evidence of two-dimensional nucleation of superconductivity in MgB2.
    EPL (Europhysics Letters) 01/2007; 59(2):272. · 2.26 Impact Factor

Publication Stats

496 Citations
192.76 Total Impact Points

Institutions

  • 2013
    • Karlsruhe Institute of Technology
      • Institute of Nanotechnology
      Carlsruhe, Baden-Württemberg, Germany
  • 1995–2013
    • Universität Augsburg
      • Institute of Physics
      Augsberg, Bavaria, Germany
  • 2002–2003
    • Kazan State Medical University
      Kasan, Tatarstan, Russia
  • 1977–2003
    • Georg-August-Universität Göttingen
      • I. Physical Institute
      Göttingen, Lower Saxony, Germany