N. Musolino

University of Geneva, Genève, GE, Switzerland

Are you N. Musolino?

Claim your profile

Publications (32)37.92 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Single crystals of (Bi1−xPbx)2Sr2Ca2Cu3O10+δ (x = 0 and 0.16) (sizes up to 3 × 2 × 0.1 mm3) have been grown by means of a newly developed “vapour-assisted travelling solvent floating zone” technique (VA-TSFZ). Post-annealing under high pressure of O2 (up to 10 MPa at T = 500 °C) was applied to enhance Tc (up to 111 K) and improve the homogeneity of the crystals (ΔTc ⩽ 1 K). The structure of both Pb-free and Pb-doped Bi-2223 was refined for the first time from single crystal X-ray diffraction (XRD) data. The unit cell of the average structure is pseudo-tetragonal with a = 5.4210(7), b = 5.4133(6) and c = 37.010(7) Å, and a = 5.395(1), b = 5.413(1) and c = 37.042(11) Å, for the Pb-free and the Pb-doped phase, respectively. An incommensurate modulation in the direction of one of the short cell vectors has been defined (q ∼ 0.21 a∗), however, the structure can be conveniently described in a supercell with a fivefold volume (a = 27.105(4) Å). With respect to the “non-modulated” structure, one additional oxygen atom for ten initial O was found to be inserted into the BiO layers. The superconducting anisotropy of Bi-2223 was found to be ∼50, from measurements of the lower critical field. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi-2212, and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.
    Current Applied Physics. 01/2008;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report a pronounced peak effect in the magnetization and the magnetocaloric coefficient in a single crystal of the superconductor Nb3Sn. As the origin of the magnetization peak effect in classical type-II superconductors is still strongly debated, we performed an investigation of its underlying thermodynamics. Calorimetric experiments performed during field sweeps at constant temperatures reveal that the sharp increase in the current density occurs concurrently with additional degrees of freedom in the specific heat due to thermal fluctuations and a liquid vortex phase. No latent heat due to a direct first-order melting of a Bragg glass phase into the liquid phase is found, which we take as evidence for an intermediate glass phase with enhanced flux pinning. The Bragg glass phase can, however, be restored by a small ac field. In this case, a first-order vortex melting transition with a clear hysteresis is found. In the absence of an ac field, the intermediate glass phase is located within the field range of this hysteresis. This indicates that the peak effect is associated with the metastability of an underlying first-order vortex melting transition.
    Physical review. B, Condensed matter 03/2007; 75(9). · 3.77 Impact Factor
  • Source
    R. Lortz, N. Musolino, Y Wang, A. Junod, N. Toyota
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a pronounced peak effect in the magnetization and the magnetocaloric coefficient in a single crystal of the superconductor Nb3Sn. As the origin of the magnetization peak effect in classical type-II superconductors is still strongly debated, we performed an investigation of its underlying thermodynamics. Calorimetric experiments performed during field sweeps at constant temperatures reveal that the sharp increase in the current density occurs concurrently with additional degrees of freedom in the specific heat due to thermal fluctuations and a liquid vortex phase. No latent heat due to a direct first-order melting of a Bragg glass phase into the liquid phase is found which we take as evidence for an intermediate glass phase with enhanced flux pinning. The Bragg glass phase can however be restored by a small AC field. In this case a first-order vortex melting transition with a clear hysteresis is found. In the absence of an AC field the intermediate glass phase is located within the field range of this hysteresis. This indicates that the peak effect is associated with the metastability of an underlying first-order vortex melting transition.
    05/2006;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The range of critical thermal fluctuations in classical bulk superconductors is extremely small and especially in low fields hardly experimentally inaccessible. With a new type of calorimeter we have been able to resolve a small lambda anomaly within a narrow temperature range around the Hc2 line. We show that the evolution of the anomaly as a function of magnetic field follows scaling laws expected in the presence of critical fluctuations. The lower onset of the fluctuation regime shows many characteristics of a continuous solid-to-liquid transition in the vortex matter. It can be driven into a first-order vortex melting transition by a small AC field which helps the vortex matter to reach equilibrium. Comment: 12 pages, 5 figures new extended version, more figures added, more detailed discussion about the vortex melting transition
    Physical Review B 04/2006; · 3.66 Impact Factor
  • Nicolas Musolino, Rolf Lortz, Alain Junod, Naoki Toyota
    [Show abstract] [Hide abstract]
    ABSTRACT: We found a sharp pronounced peak effect in the magnetization and the isothermal magnetocaloric effect of a single crystal of the classical superconductor Nb3Sn. The construction of a new type of isothermal calorimeter allowed us to study the underlying thermodynamics with an extremely high resolution. A small lambda-type anomaly could be resolved superimposed on the specific heat jump at Tc. It follows scaling laws as expected for the presence of critical fluctuations. We interpret this feature as the first clear observation of the regime of critical fluctuations in a classical superconductor. Simultaneous measurements of the specific heat and the isothermal magnetocaloric effect reveal that the peak effect occurs at the onset of fluctuations below the Hc2 line. No indications of a thermodynamic transition as the origin of the peak effect could be found. Our investigation favours thus rather a scenario in which a vortex lattice looses its topological order more continously due to the increasing strength of thermal fluctuations upon approaching the Hc2 line.
    03/2006;
  • [Show abstract] [Hide abstract]
    ABSTRACT: High quality single crystals of both Pb-free and Pb-doped Bi-2223 (with sizes up to 3×2×0.1mm<sup>3</sup>) were grown by means of a newly developed "Vapor-Assisted Travelling Solvent Floating Zone" technique in an image furnace. This technique allowed us to grow large Pb-doped Bi-2223 crystals for the first time. Post-annealing in high pressure oxygen (up to 10 MPa) enhanced T<sub>c</sub> (up to 111 K) and sharpened the superconducting transition. The crystal structures of both Bi-2223 and Bi,Pb-2223 were refined and are reported in this paper. The unit cell of the Pb-free average structure is pseudo-tetragonal with a=5.4210(7), b=5.4133(6) and c=37.009(7) Å. An incommensurate structural modulation along the direction of one of the short cell vectors has been defined (q∼0.21 a<sup>*</sup>); however, the structure can be conveniently described in a supercell with a 5-fold volume (a=27.105(4) Å). One additional O atom per translation unit of the modulation wavelength was found to be inserted into the BiO layers. Approximately 8% of the Ca sites are occupied by Bi atoms, and the refined composition is found to be Bi:Sr:Ca:Cu:O=2.16:2:1.84:3:10.16. Similar features are found in the Pb-doped phase. The magnetization of Pb-free Bi-2223 crystals has been studied. The vortex phase diagram has been traced and the anisotropy of Bi-2223 is found to be γ=53 from measurements of the lower critical field, which is much smaller than that of Bi-2212 (γ=165). Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, both of which are signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> films have been deposited using spray pyrolysis on (100) SrTiO<sub>3</sub> substrate. An extended study on the optimization of the composition, carrying gas flow, deposition temperature as well as annealing time was performed. It was found that these parameters are strongly correlated and affect the morphology, orientation and superconducting properties of the YBCO films. As grown films already exhibit J<sub>c</sub> values of 10<sup>4</sup> A/cm<sup>2</sup>, thus indicating that the correct structure is already formed during deposition. It was found that the temperature gradient in the pyrolysis zone played a fundamental role during the deposition. After modification of this heat gradient by adding a metallic susceptor, a noticeable improvement in the properties of the films was obtained. An in-plane orientation FWHM value of 0.70° was measured from the (102) pole figure. The films exhibited a T<sub>c</sub> onset of 91 K (ΔT<sub>c</sub>=1.5 K), while the J<sub>c</sub> value at 77 K in self-field approached 10<sup>5</sup> A/cm<sup>2</sup>. Based on an assumed typical intragranular critical current density, we found a 40×40 μm area in our best film where the assumed critical current density is well above 10<sup>6</sup> A/cm<sup>2</sup>.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
  • Acta Crystallographica Section A - ACTA CRYSTALLOGR A. 01/2005; 61.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The structure of Bi1.7Pb0.4Sr2Ca0.9Cu2O8 (Tc=93 K) was refined from x-ray single crystal diffraction data in space group A2aa, a=5.3852(9) Å, b=5.4286(9) Å, c=30.997(6) Å. For this composition, the crystal structure is free from the structural modulation connected with the presence of additional oxygen atoms in the BiO layers. The c-axis lattice parameter is slightly larger in (Bi,Pb)-2212 crystals than in Pb-free Bi-2212 crystals, but the complete structural refinement revealed an inhomogeneous redistribution of the inter-planar distances. In particular, the distance between the two neighboring BiO layers has significantly decreased in the modulation-free phase as compared to the Pb-free phase. We believe that this is a key point in understanding the widely observed reduction of the anisotropy in Bi-2212 by Pb-doping. The irreversibility line as well as the onset of the second magnetization peak in modulation-free (Bi,Pb)-2212 crystals were studied. Because of the strongly reduced value of the anisotropy, the 2D-3D crossover field value, Hcr, is significantly higher in (Bi,Pb)-2212 crsystals than in Bi-2212 crystals. As a direct consequence of the structural modifications induced by the removal of the modulation, the nature of the inter-layer coupling changes from electromagnetic in modulated Bi-2212 to Josephson in modulation-free (Bi,Pb)-2212. Annealing the (Bi,Pb)-2212 crystals under oxygen reintroduced the structural modulation.
    Physical review. B, Condensed matter 11/2004; 70(18). · 3.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Large and high-quality single crystals of both Pb-free and Pb-doped high temperature superconducting compounds (Bi1-xPbx)2Sr2Ca2Cu3O10-y (x = 0 and 0.3) were grown by means of a newly developed “Vapour-Assisted Travelling Floating Zone” technique (VA-TSFZ). This modified zone-melting technique was realised in an image furnace and allowed for the first time to grow Pb-doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm3 were successfully grown. Post-annealing under high pressure of O2 (up to 10 MPa at T = 500°C) was undertaken to enhance Tc and improve the homogeneity of the crystals. Structural characterisation was performed by single-crystal X-ray diffraction (XRD) and the structure of the 3-layer Bi-based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb-free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔTc ≤ 1 K). In optimally doped Pb-free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�105 A/cm2 were measured at T = 30 K and μ0H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40-50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1-5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d-wave superconductivity in Bi-2223. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Crystal Research and Technology 09/2004; 39(10):926 - 931. · 1.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Single crystals of Bi2Sr2Ca2Cu3O10 (Bi-2223) have been grown using the travelling solvent floating zone technique in an image furnace. Annealing the crystals under high pressures of O2 increased their critical temperature to 109 K, and resulted in sharp superconducting transitions of ΔTc = 1 K. The superconducting anisotropy of Bi-2223 was found to be , from measurements of the lower critical field with the magnetic field applied parallel and perpendicular to the c-axis. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi2Sr2CaCu2O8 (Bi-2212), and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.
    Superconductor Science and Technology 08/2004; 17(9):S563. · 2.76 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The magnetisation of Bi_2Sr_2Ca_2Cu_3O_10 (Bi-2223) single crystals (Tc = 109 K, DeltaTc = 1 K) has been investigated using a SQUID magnetometer. The anisotropy of Bi-2223 is found to be gamma ˜ 50 from measurements of the lower critical field, H_c1, with phHallelphc and phHallelphab. The effects of surface barriers are overcome by sweeping the magnetic field very slowly, allowing an accurate determination of H_c1 with phHallelphc from ˜100 K down to 10 K. We estimate the in-plane penetration depth to be lambda_ab(0) = 1200 ÅThe irreversibility line has been obtained from field-cooled and zero-field-cooled magnetisation data for applied magnetic fields above the second magnetisation peak. A fit to the irreversibility line is achieved using the Lindemann melting criterion for pancake vortices in a Josephson-coupled layered superconductor.
    03/2004;
  • N. Musolino, N. Clayton, R. Flükiger
    [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the vortex phase diagrams of modulation-free Bi1.7Pb0.4Sr2Ca0.9Cu2O8 crystals and Pb-free Bi2Sr2CaCu2O8+δ crystals. In (Bi,Pb)-2212 crystals, the strongly reduced anisotropy as well as the presence of a significant amount of disorder induce important differences compared to Bi-2212 crystals. We have probed the activation energies of the vortices by means of magnetic relaxation measurements, both above and below the second-magnetization peak. In the vortex phase below the peak, a power law dependence U ∝ (1/j)μ is found, with an exponent μ = 0.54 which compares favorably with the Bragg Glass prediction. In the disordered phase situated above the second-magnetization peak line, the barriers are found to slowly diverge as U ∝ ln(1/j). This suggests the existence of a glassy state in this region of the phase diagram. We have carefully measured the onset of the irreversibility in the disordered phase in both crystals. Above the 2D–3D crossover field Hcr, the resulting irreversibility lines are shown to be qualitatively described using a Lindemann approach in a 2D fluctuation regime.
    Physica C Superconductivity 01/2004; · 0.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the complete disappearance of the structural modulation in heavily lead-doped Bi2−xPbxSr2CaCu2O8+δ crystals observed by transmission electron microscopy. Crystals with a nominal lead content of x=0.8, corresponding to an effective lead content of x=0.39, yield the non-modulated phase. The superconducting properties of this modulation-free phase (β phase) have been studied and compared to those of undoped crystals displaying the modulated phase (α phase). Magnetisation measurements reveal that the irreversibility field Hirr(T) and relaxation rates are strongly improved within the β phase. Measurements of the lower critical field, Hc1, show that the anisotropy factor, ϵ, is considerably reduced in the modulation-free crystals. This is the signature of stronger coupling between CuO2 layers which in turn deeply influences the effectiveness of the pinning. These measurements explain the enhanced pinning properties in moderately Pb-doped crystals in which the α phase and β phase coexist. The enhanced pinning is not only due to the α/β interfaces, which act as effective pinning centers: the emergence of modulation-free domains, characterized by a strongly reduced anisotropy, also significantly contribute to this effect.
    Physica C Superconductivity 01/2004; 401:270-272. · 0.72 Impact Factor
  • Physica C Superconductivity 05/2003; · 0.72 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Mono- and multifilamentary Fe/MgB2 tapes and wires with high transport critical current densities have been prepared by the powder-in-tube technique using fine powders. The influence of the initial MgB2 grain size on critical current density, upper critical and irreversibility fields has been studied. After reducing the MgB2 grains to micrometer size by ball milling, the critical current density, Jc, was enhanced, while the upper critical field, μ0Hc2, remained unchanged. The anisotropy ratio between the upper critical fields parallel and perpendicular to the tape surface was determined to be 1.3, reflecting a deformation induced texture. A good agreement has been found between resistive and inductive Jc values, measured at various temperatures between 4.2 and 25 K. On monofilamentary tapes, Jc values close to 105 A cm−2 were measured at 25 K/1 T, while Jc values ≈106 A cm−2 were extrapolated for 4.2 K/0 T. Fe/MgB2 tapes exhibit high exponential n factors for the resistive transition: n values of 60 and 30 were found at 4 T and 6 T, respectively. Multifilamentary wires (with seven filaments) show slightly lower Jc values, 1.1 × 105 A cm−2 at 4.2 K/2 T. The improvement of thermal and mechanical stability of MgB2/Fe tapes and wires appears clearly as a challenge for future developments.
    Superconductor Science and Technology 01/2003; 16(2):264. · 2.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An overview of the current state of development of MgB2 wires and tapes prepared by several techniques is presented, based on the known literature data and our own results. We focus on the powder-in-tube processing method, using pre-reacted MgB2 powders surrounded by an Fe sheath (ex situ processing route). The study of the effect of the initial MgB2 particle size shows that after reducing the initial particles by ball milling to sizes of the order of 3 μm, the degree of texturing and the upper critical field, Bc2, remain unchanged, while both the critical current density, Jc, and the irreversibility field, Birr, show a considerable increase, followed by a decrease after longer milling times. After various recrystallization times and temperatures we show that a critical amount of impurities introduced during the particle reduction process is responsible for the observed maximum of Jc and Birr. Our analysis indicates that this is a grain boundary effect, thus pointing the way for further improvement of the transport properties. A preferential orientation along the c-axis has been observed in Fe/MgB2 tapes by X-ray diffraction. An anisotropy ratio of 1.3 for both Bc2 and Birr was found. The Fe/MgB2 tapes exhibit a very high n factor, which opens up the possibility for a persistent mode operation at 4.2 K and moderate fields. Transport Jc values above 104 A/cm2 are obtained in monofilamentary Fe/MgB2 tapes at 4.2 K and 6.5 T and at 25 K and 2.25 T. Multifilamentary tapes were found to exhibit lower Jc values due to the presently used deformation process yielding a lower density with respect to monofilaments. In all measured tapes, quenching was observed at the lowest applied fields. Improvement of the thermal stability of MgB2 tapes will be one of the major challenges in future developments.
    Physica C Superconductivity 01/2003; · 0.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the complete disappearance of the structural modulation in heavily lead-doped Bi2−xPbxSr2CaCu2O8+δ crystals observed by transmission electron microscopy. Crystals with a nominal lead content of x=0.8, corresponding to an effective lead content of x=0.39, yield the non-modulated phase. The superconducting properties of this modulation-free phase (β phase) have been studied and compared to those of undoped crystals displaying the modulated phase (α phase). Magnetisation measurements reveal that the irreversibility field Hirr(T) and relaxation rates are strongly improved within the β phase. Measurements of the lower critical field, Hc1, show that the anisotropy factor, ϵ, is considerably reduced in the modulation-free crystals. This is the signature of stronger coupling between CuO2 layers which in turn deeply influences the effectiveness of the pinning. These measurements explain the enhanced pinning properties in moderately Pb-doped crystals in which the α phase and β phase coexist. The enhanced pinning is not only due to the α/β interfaces, which act as effective pinning centers: the emergence of modulation-free domains, characterized by a strongly reduced anisotropy, also significantly contribute to this effect.
    Physica C Superconductivity 01/2003; · 0.72 Impact Factor
  • Source
    Physica C-superconductivity and Its Applications - PHYSICA C. 01/2003; 387(3):419-419.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Dense pure and doped (Mg1 – x A x )B2 samples with A = Na, Ca, Cu, Ag, Zn, and Al were synthesized at high pressure–high temperature in a multi-anvils press (3.5–6 GPa, 900–1000C) for 0 x 0.20. They were studied by X-ray diffraction, scanning electron microscopy and their superconducting properties were investigated by AC susceptibility, magnetization, and transport measurements. Only Al is really substituted on the Mg site. The other elements form secondary phases with B or Mg. No large effect is observed on the superconducting properties T c, j c critical current, H irr, and H c2.
    Journal of Superconductivity 11/2002; 15(6):613-619.