Superconductor YBa2Cu3O7 Research Articles

Magnetically induced anisotropy of flux penetration into strong-pinning superconductor/ferromagnet bilayers

We studied the impact of soft ferromagnetic permalloy (Py) on the shielding currents in a strong-pinning superconductor—YBa2Cu3O7−δ with Ba2Y(Nb/Ta)O6 nano-precipitates—by means of scanning transmission x-ray microscopy. Typically and in particular when in the thin film limit, superconductor/ferromagnet (SC/FM) bilayers exhibit isotropic properties of the flux line ensemble at all temperatures. However, in elements with small aspect ratio a significant anisotropy in flux penetration is observed. We explain this effect by local in-plane fields arising from anisotropic magnetic stray fields originated by the ferromagnet. This leads to direction-dependent motion of magnetic vortices inside the SC/FM bilayer. Our results demonstrate that small variations of the magnetic properties can have huge impact on the superconductor.

Evaluation of gamma attenuation parameters and kerma coefficients of YBaCuO and BiPbSrCaCuO superconductors using EGS4 code

The levels of the coefficients of the mass attenuation (μ/ρ) for YBaCuO and BiPbSrCaCuO superconductors and their contents were determined theoretically, using EGS4 simulation code and the XCOM database, and experimentally at gamma-ray energies of 511, 661 and 1274 keV. Additionally, radiation attenuation parameters such as half value layer (HVL), mean free path (MFP) and effective atomic number (Zeff) for investigated superconductors samples were calculated using the obtained μ/ρ values. It was observed that the theoretical and the experimental values were in agreement. Furthermore, the gamma-ray kerma coefficient k of these elements and superconductor samples was evaluated theoretically and experimentally, based on results of the mass attenuation coefficients determined at the same energies, and good agreement was observed. The theoretical levels of these coefficients were also computed over an expanded energy interval from 1 keV to 100 MeV using the WinXCom program. The results show that the calculated gamma kerma coefficient values of BiPbSrCaCuO had the highest atomic number, which was higher than for the YBaCuO superconductor.

Series arrays of planar long Josephson junctions for high dynamic range magnetic flux detection

We investigated series arrays of closely spaced, planar long Josephson junctions for magnetic field transduction in Earth’s field, with a linear response and high dynamic range. The devices were fabricated from thin film high-temperature superconductor YBa2Cu3O7−δ (YBCO) thin films, using focused helium ion beam irradiation to create the Josephson barriers. Four series arrays, each consisting of several hundreds of long junctions, were fabricated and electrically tested. From fits of the current-voltage characteristics, we estimate the standard deviation in critical current to be around 25%. Voltage-magnetic field measurements exhibit a transfer function of 42 mV/mT and a linear response over a range of 303 μT at 71 K, resulting in a dynamic range of 124 dB.

Thermodynamic Properties of Stoichiometric Non-Superconducting Phase Y2BaCuO5.

Y2BaCuO5 often occurs as an accompanying phase of the well-known high-temperature superconductor YBa2Cu3O7 (also known as YBCO). Y2BaCuO5, easily identifiable due to its characteristic green coloration, is often referred to as ‘green phase’ or ‘Y-211’. In this contribution, Y2BaCuO5 phase was studied in detail with a focus on its thermal and thermodynamic properties. Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed in the study of sample’s morphology and chemical composition. XRD data were further analyzed and lattice parameters refined by Rietveld analysis. Simultaneous thermal analysis was employed to study thermal stability. Particle size distribution was analyzed by laser diffraction. Finally, thermodynamic properties, namely heat capacity and relative enthalpy, were measured by drop calorimetry, differential scanning calorimetry (DSC), and physical properties measurement system (PPMS). Enthalpy of formation was assessed from ab-initio DFT calculations.

Dynamics of Abrikosov’s Vortex Forced Oscillations: Role of Frequency, Acting Forces and Vortex Parameters

The trajectories of motion of an isolated Abrikosov vortex in the anisotropic YBa2Cu3O7 superconductor under the influence of an external periodic force, damping into the sample, were constructed and analysed, taking into account the inert properties of the vortex and the forces acting on it: pinning, Lorentz, elasticity and viscosity. The hierarchy of the influence of various forces in a wide frequency range (∼1 THz) of the driving force on the shape and size of the trajectory is established. The calculated energy absorption by the vortex, as a function of frequency, taking into account the effective mass of the vortex, has resonant peaks: one at low frequency, associated with the de Gennes and Matricon mode, and the second at high frequency. The differences, manifested in vortex-induced oscillations for different field orientations in YBa2Cu3O7 and for the isotropic low-temperature superconductor NbTi, are analysed.

Investigation of magnetic force properties between different PMGs and multi-seeded YBCO superconductors with different seed distances

The magnetic levitation force in vertical direction and guidance force in lateral direction should be increased for enhancing the loading capacity and stability of Maglev systems, respectively. In this study, we have produced multi‒seeded YBCO (YBa2Cu3O7) superconductors with two seeds and investigated the effect of seed distance on the vertical levitation force and lateral guidance force properties by using different permanent magnetic guideway (PMG) arrangements. Although there are studies in literature related to different distance, orientation and angle of seeds; there is no detailed study investigating the effect of seed distance on the vertical and lateral magnetic force properties of Maglev systems depending on different types of PMGs. In this study, after the sample fabrication, the optimum PMG arrangement were determined by using numerical simulation to obtain magnetic flux density distribution. It is determined that both maximum levitation and guidance force values firstly increased with increasing the seed distance from 0 to 4 mm and then related forces decreased with increasing the seed distance from 4 to 16 mm but still keep the higher force values than the sample with the seed distances of 0 mm. This situation is clarified as the increasing of the seed distance to an optimum value enhances both the levitation and guidance forces simultaneously and this is very important for levitation force applications because it causes to easy control of the Maglev system in vertical and lateral directions.

Comparative Investigation on Magnetic Behavior of Partial Rare Earth Element (Re: Lu, Yb, and Dy) Substituted Y0.5Re0.5BCO (123) Superconductors

Partial Re (rare earth elements: Lu, Yb and Dy) substituted YBaCuO (123) superconductors synthesized by solid-state reaction (SSR) procedure have been investigated via x-ray diffraction, scanning electron microscopy, a.c. magnetic susceptibility, and d.c. magnetization, and calculations. The measurements of a.c. magnetic susceptibility have been carried out at constant a.c. field amplitude and constant frequency for the samples studied. The temperature dependence of intergranular critical current density (Jcm) has been estimated from the a.c. magnetic susceptibility data. The d.c. magnetization measurements were performed at the temperatures of 5 K, 20 K, and 77 K separately. The variation of critical current density (Jc) with magnetic field (μ0H) has been evaluated from the d.c. magnetization data by using upper and lower branch of the major hysteresis curve. Lu substituted Y0.5Lu0.5BCO (123) sample shows higher critical current density than Yb and Dy substituted samples at low-temperature (lower than 77 K) regions.

π-Loops With ds Josephson Junctions

We fabricated Josephson junctions (JJs) between the d-wave superconductor (SC) YBa 2 Cu 3 O 7 -x (YBCO) and the swave SC Nb (ds-JJs) on graphoepitaxially buffered MgO substrates, studied ds-JJs at temperatures down to 30 mK and employed these JJs in π-loops. Current-voltage characteristics of dsJJs oriented along the [100] axis of YBCO exhibited up to a factor of 200 higher critical current densities than ds-JJs oriented along the [110] axis of YBCO. The critical current I and the IcRn product of [100]-oriented 3 μm wide ds-JJs are ~70 μA and ~200 μV, respectively, at 4.2 K. Rectangular arrays of up to 40 000 π-loops based on such ds-JJs were investigated using a low temperature scanning superconducting quantum interference device (SQUID) microscope. We observed ordering of spontaneously generated half integer magnetic flux quanta in the π-loops correlated with minute spurious background magnetic fields, as well as with configurations and mutual coupling of the π-loops. We manipulated the magnetic states of the π-loops by the local application of magnetic fields using nearby planar coils. This paper paves the way for the use of π-loops in computations that are based on annealing processes.

Magnetic levitation and guidance performance of Y–Ba–Cu–O and Gd–Ba–Cu–O bulk superconductors under low ambient pressure

The high-temperature superconducting Maglev-evacuated tube transport (HTS Maglev-ETT) system has significant potential for practical applications. In order to employ HTS bulks in an ETT system, it is necessary to study the magnetic levitation and guidance performance of bulk superconductors under low ambient pressure conditions that are representative of those inside the tube. As a result, we have investigated the Maglev performance of Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) single grain, bulk superconductors under different ambient pressures of 100 kPa, 60 kPa and 20 kPa using a bespoke pressure-controlling platform, in which the superconductors were positioned above a Halbach permanent magnet guideway. The levitation forces under conditions of field-cooling (FC) and zero-field-cooling (ZFC) have been measured and analyzed. The guidance force for the FC case and the levitation force relaxation for the ZFC case were also measured. It was found from the experimental results that the Maglev performance of both types of bulk superconductor improves significantly by reducing the ambient pressure in their immediate working environment. The levitation forces of YBCO and GdBCO bulk superconductors were observed to increase by 11.6% and 4.4% in the case of FC, and by 20.3% and 13.7% in the case of ZFC, respectively, as the ambient pressure changed from 100 kPa to 20 kPa. An improvement of the guidance force and an inhibition of the levitation force relaxation were also observed for these materials. The supercooled liquid nitrogen cryogen in the low-pressure environment further reduces the temperature, which, in turn, increases the critical current density Jc of the bulk superconductors and improves their levitation performance. These results provide further evidence of the significant advantages of combining HTS Maglev with evacuated tube technologies as a key enabling feature of the HTS Maglev-ETT system. The data further indicate that YBCO bulk superconductors tend to be more sensitive to ambient pressure and temperature variation than GdBCO bulk superconductors. This difference essentially reflects the dependence of Maglev performance of HTS bulk superconductors on Jc when operating in a low-pressure environment.

Memory-functionality superconductor/ferromagnet/superconductor junctions based on the high- Tc cuprate superconductors YBa2Cu3O7−x and the colossal magnetoresistive manganite ferromagnets La2/3X1/3MnO3+δ(X=Ca,Sr)

Complex oxides exhibit a variety of unusual physical properties, which can be used for designing novel electronic devices. Here we fabricate and study experimentally nano-scale Superconductor/ Ferromagnet/Superconductor junctions with the high-Tc cuprate superconductor YBa2Cu3O7 and the colossal magnetoresistive (CMR) manganite ferromagnets LaXMnO3 (X: Ca or Sr). We demonstrate that in a broad temperature range the magnetization of a manganite nanoparticle, forming the junction interface, switches abruptly in a mono-domain manner. The CMR phenomenon translates the magnetization loop into a hysteretic magnetoresistance loop. The latter facilitates a memory functionality of such a junction with just a single CMR ferromagnetic layer. The orientation of the magnetization (stored information) can be read out by simply measuring the junction resistance in an applied magnetic field. The CMR facilitates a large read-out signal in a small applied field. We argue that such a simple single layer CMR junction can operate as a memory cell both in the superconducting state at cryogenic temperatures and in the normal state up to room temperature.

Growth and Nanofabrication of All-Perovskite Superconducting/Ferromagnetic/Superconducting Junctions

We fabricate and study experimentally all-perovskite-oxide superconductor/ferromagnetic insulator/superconductor (S/FI/S) tunnel junctions made out of the high-temperature cuprate superconductor YBa2Cu3O7−y (YBCO) and the colossal magnetoresistive manganite LaMnO3 (LMO) in the ferromagnetic insulator state. YBCO/LMO/YBCO heterostructures with different LMO thicknesses (5, 10, and 20 nm) are grown epitaxially via pulsed laser deposition. Nanoscale S/FI/S junctions with sizes down to 300 nm are made by three-dimensional nano-sculpturing with focused ion beam. Junctions with a thick (20 nm) LMO barrier exhibit a large negative magnetoresistance below {T}_{Curie}sim 160 K, typical for colossal magnetoresistive manganites, as well as a kink in the current-voltage characteristics at large bias ( Vsim 1 –2 Volts), attributed to Zener-type tunneling. However, they do not show a measurable Josephson current. On the contrary, junctions with the thinnest 5-nm LMO barrier exhibit a large supercurrent and no signs of magnetism. The latter may indicate the presence of pinholes due to thickness inhomogeneity and/or a sim 2 nm dead magnetic layer at the YBCO / LMO interface caused, e.g., by interdiffusion or strain. The junction with an intermediate 10-nm LMO barrier exhibited a desired S/FI/S junction behavior with significant negative magnetoresistance and signatures of a small Josephson current.

The remarkable difference in water wettability of YBa2Cu3O7−x and Y2BaCuO5 powders

The irreversible deterioration in superconducting performance caused by the reactions with air moisture is a severe obstacle for the applications of Y-Ba-Cu-O (YBCO) superconductors. However, the detailed water adsorption mechanism and the crack growth behaviors in superconductors are still not very clear. In this study, YBa2Cu3O7−x (Y123) and Y2BaCuO5 (Y211) powders are fabricated by chemical coprecipitation method for experiments. An optical contact angle measuring device is used to analyze the water wettability of powders. The results demonstrate that Y123 powders are super hydrophilic while Y211 powders are hydrophobic. The concomitant difference in surface energy of powders results in a large number of crystal spaces between Y211 particles and Y123 grain domain after crystal growth. Such crystal spaces are the vulnerable parts for air moisture. A deterioration and crack-growth mechanism of YBCO superconductors under air moisture is proposed and discussed accordingly.

Magnetic Moment of Melted YBaCuO Superconducting Bulk.

YBaCuO superconductor with variations in the BaZrO₃ content was fabricated via thermal diffusion, to study the changes in its electrical properties and superconducting behavior. While the critical temperature of the YBaCuO superconductor did not predominately depend on the BaZrO₃ content, the addition of BaZrO₃ formed a pinning center for the magnetic BaZrO₃, which effected a change in the electromagnetic properties of the YBaCuO superconductor. This result indicates that magnetization is proportional to the number of magnetic flux lines passing through the superconductor.

Activation energy of oxygen diffusion: A possible indicator of supercurrents through YBa2Cu3O7 grain boundaries

Oxygen diffusion is the main transportation form during the preparation process of polycrystalline superconductor YBa2Cu3O7 (YBCO) thin films. Especially the diffusion of oxygen ions in grain boundaries (GBs) can lead to the formation of oxygen vacancies, and finally have an impact on the critical current density (Jc) of YBCO conductors. To deeply understand the supercurrent-limiting mechanism of GBs, for an YBCO bicrystal (containing a single GB), in this article we intensively studied the diffusion of oxygen ions through GB region by molecular dynamics simulations. The calculated results show that the oxygen diffusion in the YBCO bicrystals can be enhanced in GBs, and specifically which is closely related to the grain boundary angle (θ). The most interesting finding is that the activation energy of oxygen diffusion shows an exponential fall with the grain boundary angle, which is exactly consistent with the relation of the critical current density versus the grain boundary angle (Jc ~ θ) in GBs. We firmly believe that the activation energy of oxygen diffusion should have an essential relevance with the Jc especially in YBCO GBs, and can be as an indicator for predicting supercurrents. For these results we further gave an in-depth discussion.

Probing the electric field-induced doping mechanism in YBa2Cu3O7 using computed Cu K-edge x-ray absorption spectra.

We recently demonstrated that the superconductor-to-insulator transition induced by ionic liquid gating of the high temperature superconductor YBa2Cu3O7 (YBCO) is accompanied by a deoxygenation of the sample [A. M. Perez-Munoz et al., Proc. Natl. Acad. Sci. U. S. A. 114, 215 (2017)]. Density functional theory calculations helped establish that the pronounced changes in the spectral features of the Cu K-edge absorption spectra measured in situ during the gating experiment arise from a decrease of the Cu coordination within the CuO chains. In this work, we provide a detailed analysis of the electronic structure origin of the changes in the spectra resulting from three different types of doping: (i) the formation of oxygen vacancies within the CuO chains, (ii) the formation of oxygen vacancies within the CuO2 planes, and (iii) the electrostatic doping. For each case, three stoichiometries are studied and compared to the stoichiometric YBa2Cu3O7, i.e., YBa2Cu3O6.75, YBa2Cu3O6.50, and YBa2Cu3O6.25. Computed vacancy formation energies further support the chain-vacancy mechanism. In the case of doping by vacancies within the chains, we study the effect of oxygen ordering on the spectral features and we clarify the connection between the polarization of the x-rays and this doping mechanism. Finally, the inclusion of the Hubbard U correction on the computed spectra for antiferromagnetic YBa2Cu3O6.25 is discussed.

Uniaxial pressure control of competing orders in a high-temperature superconductor.

Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa2Cu3O6.67 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the a axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials.

Synthesis of Y2BaCuO5 nano-whiskers by a solution blow spinning technique and their successful introduction into single-grain, YBCO bulk superconductors

The ability of single grain Y-Ba-Cu-O (YBCO) bulk superconductors to trap large magnetic fields is due generally to the presence of embedded, non-superconducting Y2BaCuO5 (Y-211) phase particles, in optimum amount, in the superconducting YBa2Cu3O7-δ (Y-123) phase matrix, which increases flux pinning and, hence, critical current density of the bulk material. The presence of smaller particles of Y-211 could be expected to improve further the superconducting properties of single grain, bulk YBCO samples, although the smallest Y-211 particles that have been engineered to date within the bulk microstructure are around 800 nm in size. It is extremely challenging to reduce the Y-211 particle size any further due to problems of particle agglomeration that originate, inevitably, from the effects of surface energy and reactivity at relatively high processing temperatures. In this work, we report a novel approach to the fabrication of Y-211 pinning centres in bulk YBCO superconductors in the form of nano-whiskers manufactured by a solution blow spinning technique. The Y-211 nano-whiskers, of which 62% were smaller than 500 nm, were added to the YBCO precursor powders to produce a single grain bulk sample by the buffer-aided top-seeded melt growth (BA-TSMG) processing technique. The resulting YBCO single grain, of diameter 20 mm, was able to trap a magnetic field of 0.63 T at 77 K with an associated critical current density of 3.9 × 104 A/cm2 in self-field. The results of this study demonstrate clearly that the use of Y-211 nano-whiskers is a promising route for enhancing flux pinning in bulk YBCO single-grains, which is potentially significant for the development of high field engineering applications.

Radiative Transfer, Non-transparency, Stability Against Quench in Superconductors and Their Correlations

Radiative transfer calculations are presented for multi-filamentary BSCCO 2212 and 2223 and for thin film-coated YBaCuO 123 superconductors. A strictly radiative view allows conductor morphology of these superconductors to be interpreted as particulate or quasi-particulate objects. Problems then arising from non-regular particle shape, missing refractive indices, dependent scattering and superconductor material (diamagnetic) properties are solved in a multi-step, approximation approach. Both types of conductors are shown to be non-transparent to mid-IR radiation. Non-transparency may become critical for superconductor stability. The obtained extinction cross sections converge near the phase transition. A substantial difference of extinction properties between the superconducting and normal conducting state thus cannot be observed. As a first corollary from non-transparency, application of the additive approximation for the total thermal conductivity used in previous numerical calculations of the BSCCO and YBaCuO superconductors is confirmed. Second, within transit time intervals, the length of which depends on optical thickness, no uniform equilibrium conditions of electron pair density within the conductor cross section and near critical temperature are observed. Phase transition does not proceed uniformly, neither spatial nor temporal, and the order (succession on time scales) of local events (temperature variations, quench), in extreme cases, is completely dissolved. As another corollary, non-transparency even makes the existence of uniquely defined, physical time scales doubtful in a superconductor. The obtained results are expected to improve existing stability models and will be of practical value for future materials development.

Inverse Magnetoresistance Characteristic of Hybrid-Type Multilayer Structure of IrMn-Based Giant-Magnetoresistance Spin Valve and High-Tc Superconductor YBa2Cu3O7−x Film

An antiferromagnetic-IrMn-based giant-magnetoresistance spin-valve (GMR-SV) multilayer on a high-temperature superconductor YBa2Cu3O7−x (YBCO) film was prepared using an ion-beam deposition system. The exchange bias coupling field (Hex), coercivity (HC), and magnetoresistance ratio (MR (%)) of the hybrid YBCO/GMR-SV multilayer structure were measured and compared at room temperature and 77 K. The MR ratio (%) of the hybrid YBCO/GMR-SV structure measured by the four-probe method at 77 K was − 9.3%, different from that of the conventional GMR-SV structure. The phenomenon of a negative MR (%) below the critical temperature (Tc) can be explained by the current-in-plane tunneling effect, when the resistance of the middle gap (G) layer between the high-temperature superconductor YBCO and GMR-SV multilayer reaches a value comparable to the plane resistance of the upper metal layer. In order to analyze the inversed MR (%) of the hybrid YBCO/GMR-SV multilayer structure, the equivalent circuit for each layer was constructed and an equation of the output voltage was derived.

Differential equations for recovery of the average differential susceptibility of superconductors from measurements of the first harmonic of magnetization

In the paper, inhomogeneous differential equations are obtained to reconstruct the average differential susceptibility of type-II superconductors from the in-phase (real) component of the magnetization’s first harmonic in the hysteresis case. Basing on the second-order differential equation, mathematical modeling of the average differential susceptibility for the theoretical and experimental dependence of the real part of the magnetization’s first harmonic is performed. The Cauchy problem was solved numerically by the Runge-Kutta method of the fourth order of accuracy. To do this, the differential equation for the restoration of the average susceptibility was reduced to a system of differential equations. On the basis of the method developed in the work, the average differential susceptibility of a disc-shaped polycrystalline superconductor YBa2Cu3O7−x was reconstructed from the experimentally obtained first harmonic of magnetization in interval of magnetic fields from 0 to 800 Oe.