Top-down and bottom-up through-thickness current anisotropy in a bilayer YBa2Cu3O7−x film (original) (raw)
Related papers
Applied Physics Letters, 2007
The authors find the critical current anisotropy of a bilayer YBa 2 Cu 3 O 7−␦ film with different pinning structures in each layer is the sum of the anisotropy of the two individual layers, revealing that it is possible to tune the anisotropy of the composite through variation of an individual layer's thickness and pinning structure. YBa 2 Cu 4 O x intergrowths and Dy 2 O 3 nanodots were the dominant pinning structures in the top and bottom layers, respectively. The bottom layer of the composite was isolated using traditional Ar + ion milling and the top layer was isolated using a focused ion beam, allowing each layer to be studied independently.
Thin Solid Films, 2010
We have fabricated and studied quasi-multilayered thick YBa 2 Cu 3 O 7 − δ (YBCO) films composed of several YBCO layers interspaced with quasi-layers of non-superconducting YBa 2 Cu 3 O x nanodots, grown by Pulsed Laser Deposition on SrTiO 3 (100) substrates. Magnetization J c (B) at 77.3 K for these thick films showed significant improvement as compared to pure YBa 2 Cu 3 O 7 − δ films of same or even smaller thickness. A high J c (B) in our quite thick films (1 μm to 6 μm) provides a very high total critical current per centimetre of the film width, I c − w . Critical current as high as 830 A per cm width in self field and 77.3 K was achieved in 5 μm thick quasi-multilayer film with non-superconducting YBa 2 Cu 3 O x nanodots. Frequency-dependent susceptibility measurements showed also an increase in the pinning potential. The angular dependence of I c − w at 86.5 K, in 3 T shows a clear indication of anisotropic pinning centres aligned along the c-direction.
Superconductor Science and Technology, 2005
Nanodot arrays of Y 2 O 3 were dispersed in thin films of YBa 2 Cu 3 O 7−δ (YBCO) by growing alternating layers of these two species using a pulsed laser deposition method. As a result, critical current density J c both in applied magnetic field and self-field is enhanced by as much as an order of magnitude, along with a significant increase in the irreversibility field H irr . High-resolution scanning transmission electron microscopy (STEM) and Z -contrast STEM show that the nanoparticles are crystalline and coherent with the YBCO matrix. Whereas in most other studies pinning has been attributed to the strain fields around the nanoparticles, in this case pinning may actually be due to the nanoparticles themselves, since the delineation between the two species is very sharp and STEM reveals no discernible strain fields in the superconducting material around the nanoparticles.
Multilayering approach to enhance current carrying capability of YBa2Cu3O7 films
2010
High temperature superconducting (HTS) thin films deposited onto metallic substrates are known as coated conductors (CC) and are currently the most promising HTS candidates for wide-scale industrial applications. These films are fabricated from ReBa2Cu3O7 (where Re is a rare earth element) ceramics and have very specific requirements with regard to their manufacturing and maintenance, due to their complex stoichiometry and large anisotropy. One of the most important problems studied by many researchers around the world is the improvement of critical current capability in such superconducting films. Structures consisting, for example, of both YBa2Cu3O7 (YBCO) layers and layers of different superconductive or nonsuperconductive materials having a similar crystal structure are likely to have enhanced microstructural properties, and they are able to carry larger critical currents as compared to their monolayer counterparts. Such sandwich-like films are called multilayer structures. Usua...
Superconductor Science & Technology, 2005
Nanodot arrays of Y 2 O 3 were dispersed in thin films of YBa 2 Cu 3 O 7−δ (YBCO) by growing alternating layers of these two species using a pulsed laser deposition method. As a result, critical current density J c both in applied magnetic field and self-field is enhanced by as much as an order of magnitude, along with a significant increase in the irreversibility field H irr . High-resolution scanning transmission electron microscopy (STEM) and Z -contrast STEM show that the nanoparticles are crystalline and coherent with the YBCO matrix. Whereas in most other studies pinning has been attributed to the strain fields around the nanoparticles, in this case pinning may actually be due to the nanoparticles themselves, since the delineation between the two species is very sharp and STEM reveals no discernible strain fields in the superconducting material around the nanoparticles.
Scientific Reports, 2016
The addition of mixed double perovskite Ba 2 Y(Nb/Ta)O 6 (BYNTO) to YBa 2 Cu 3 O 7−δ (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m 3 at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.
We report on the thickness dependence of the superconducting characteristics including critical current I c , critical current density J c , transition temperature T c , irreversibility field H irr , bulk pinning force plot F p (H), and the normal state resistivity curve ρ(T) measured after successive ion milling of ~ 1 µm thick high I c YBa 2 Cu 3 O 7-x films made by an ex situ metal-organic deposition process on Ni-W rolling-assisted biaxially textured substrates (RABiTS TM ). Contrary to many recent data, mostly on in situ pulsed laser deposition (PLD) films, which show strong depression of J c with increasing film thickness t, our films exhibit only a weak dependence of J c on t. The two better textured samples had full cross-section average J c,avg (77K,0T) ~ 4 MA/cm 2 near the buffer layer interface and ~3 MA/cm 2 at full thickness, despite significant current blocking due to ~30% porosity in the film. Taking account of the thickness dependence of the porosity, we estimate that the local, vortex-pinning current density is essentially independent of thickness, while accounting for the additional current-blocking effects of grain boundaries leads to local, vortex-pinning J c values well above 5 MA/cm 2 . Such high local J c values are produced by strong three-dimensional vortex pinning which subdivides vortex lines into weakly coupled segments much shorter than the film thickness. which levels off above a critical thickness t c ~ 1 µm [2-9]. Such a thickness dependence is suggestive of the transition from the 2 dimensional (2D) pinning of rigid vortex lines in films thinner than the longitudinal pinning correlation length l c to the 3-dimensional (3D) pinning of deformable vortices at t > t c [14]. It was recently pointed out [15] that t c can indeed approach a few µm if the collective pinning model incorporates a multi-scale pinning potential appropriate for the strong-pinning second phase precipitates, pores, and correlated defects found in CCs. Strong-pinning defects have a pin interaction range, r p much greater than the coherence length ξ and produce large plastic deformations of vortices, rather than the small elastic deformations produced by weak, point pins. This strong-pinning model predicts a crossover thickness t c as large as 1-2 µm, in agreement with the observed J c (t) dependence of many PLD films [2-8] and qualitatively consistent with many recent studies of the angular dependence of 3 J c in CCs, which also reveal much evidence for correlated pinning along the c-axis in PLD films . This multiscale pinning model also predicts the t -1/2 thickness dependence of J c (t), but the magnitudes of J c and t c can be very dependent on the specific pinning microstructure and thus on the film growth process.
Increased critical current density and pinning in thick Ag/YBa2Cu3O7−x multilayers
Physica C: Superconductivity, 2010
We have investigated the superconducting properties of Ag/YBa 2 Cu 3 O 7Àx thick multilayers grown by Pulsed Laser Deposition, and found that the artificial pinning centres induced by Ag nanodots lead to a significant increase in critical current, especially in high applied magnetic fields. Transmission Electron Microscopy showed a columnar growth of YBa 2 Cu 3 O 7Àx induced by Ag nanodots, while angle-dependent transport measurements revealed the existence of strong, both isotropic and c-axis correlated, artificial pinning centres.
Pinning potential in thick PrBa2Cu3Ox/YBa2Cu3O7-delta quasi-multilayers
Physica C-Superconductivity and Its Applications, 2010
Using Pulsed Laser Deposition we have fabricated thick quasi-multilayers composed of incomplete layers of PrBa 2 Cu 3 O x (PrBCO) nano-dots and layers of YBa 2 Cu 3 O 7Àd (YBCO). The number of such sequences was between 2 and 6, with the thickness of individual YBCO layers between 565 and 885 nm, and total thickness between 1.13 and 5.31 lm. For the thinner quasi-multilayer, DC magnetization studies showed an increase in the critical current density J c at all fields in comparison with a pure YBCO reference sample, while the thicker samples showed an increased J c only in high fields. We have also investigated the frequency dependence of J c from AC susceptibility studies and found that the pinning potential is well described by a logarithmic dependence on current density. Pinning potentials in PrBCO/YBCO quasi-multilayers also proved to be higher than in the reference sample at high fields. From angle-dependent transport measurements we have found indications of strong pinning centres induced by the (PrBCO) nanodots, both isotropic and c-axis correlated.
Applied Physics Letters, 1991
We have measured the transport critical current density (J,) in epitaxial quality films of YBa2Cuj07 _ 6 some of which were covered by thin (10 nm) Ag films. The films, both with and without Ag, had J, values greater than IO6 A/cm2 in liquid nitrogen. The effect of the Ag was to greatly reduce the dependence of J, on external magnetic fields in the case where the field was oriented in the plane of the film, that is, perpendicular to the c axis. It is unlikely that the effect is simply due to altered surface pinning, although qualitative agreement with critical state models is observed.