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By controlling the early stages of thin film growth during laser ablation (i.e. Volmer–Weber type growth), we have synthesized magnetic nanocomposites consisting of nickel (Ni) nanoparticulates in multiple layers of yttria stabilized zirconia. The magnetic properties are a strong function of the nickel particle size, showing a clear transition from superparamagnetic to ferromagnetic characteristics. The coercivity at 300 K varies from 0 to nearly 13 kA m − 1 (∼ 160 Oe) as the laser ablation time is increased. By applying the Scherrer formula to X-ray diffraction patterns, we estimated the average size of the Ni nanoclusters to be

By controlling the early stages of thin film growth during laser ablation (i.e. Volmer–Weber type growth), we have synthesized magnetic nanocomposites consisting of nickel (Ni) nanoparticulates in multiple layers of yttria stabilized zirconia. The magnetic properties are a strong function of the nickel particle size, showing a clear transition from superparamagnetic to ferromagnetic characteristics. The coercivity at 300 K varies from 0 to nearly 4 A m − 1 (∼ 300 Oe) as the laser ablation time is increased. By applying the Scherrer formula to X-ray diffraction patterns, we estimated the average size of the Ni nanoclusters to be

The physical and electrical characteristics of oxide buffer layers for Cu-based coated conductors are reviewed, with emphasis on the need for conductive buffers and advanced Cu-based substrates. Methods for preventing Cu oxidation are discussed because it is an anticipated problem for applications using Cu-based rolling assisted biaxially textured substrates (RABiTS).

The development of biaxially textured, second-generation, high-temperature superconducting (HTS) wires is expected to enable most large-scale applications of HTS materials, in particular electric-power applications. For many potential applications, high critical currents in applied magnetic fields are required. It is well known that columnar defects generated by irradiating high-temperature superconducting materials with heavy ions significantly enhance the in-field critical current density. Hence, for over a decade scientists world-wide have sought means to produce such columnar defects in HTS materials without the expense and complexity of ionizing radiation. Using a simple and practically scalable technique, we have succeeded in producing long, nearly continuous vortex pins along the c-axis in YBa2Cu3O7?? (YBCO), in the form of self-assembled stacks of BaZrO3 (BZO) nanodots and nanorods. The nanodots and nanorods have a diameter of ~2?3?nm and an areal density ('matching field') of 8?10?T for 2?vol.% incorporation of BaZrO3. In addition, four misfit dislocations around each nanodot or nanorod are aligned and act as extended columnar defects. YBCO films with such defects exhibit significantly enhanced pinning with less sensitivity to magnetic fields H. In particular, at intermediate field values, the current density, Jc, varies as Jc~H??, with ?~0.3 rather than the usual values 0.5?0.65. Similar results were also obtained for CaZrO3 (CZO) and YSZ incorporation in the form of nanodots and nanorods within YBCO, indicating the broad applicability of the developed process. The process could also be used to incorporate self-assembled nanodots and nanorods within matrices of other materials for different applications, such as magnetic materials.

Nanodot arrays of Y2O3 were dispersed in thin films of YBa2Cu3O7−δ (YBCO) by growing alternating layers of these two species using a pulsed laser deposition method. As a result, critical current density Jc 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 Hirr. 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 ,s incethe delineation between the two species is very sharp and STEM reveals no discernible strain fields in the superconducting material around the nanoparticles. (Some figures in this article are in colour only in the electronic version)

The growth of 0.9–1.0 µm thick Y Ba2Cu3O7−δ (YBCO) films on biaxially textured Ni–3 at.% W (NiW) substrates using the BaF2 ex situ process was investigated at reduced pressures. By varying the water vapour pressure (PH2O), Y–BaF2–Cu–O (YBFCO) precursor films deposited by e-beam co-evaporation were converted at a reduced total pressure (Ptotal) of 50–55 Torr and conversion temperature (TS) of 740 °C for a wet conversion time (tW) of 60 min. Critical current density (JC) values greater than 1 MA cm−2 for the thick YBCO films were obtained under the condition of varying PH2O from low pressure to 10 Torr. The transition temperatures (TC) of the samples were over 90 K with ΔTC = 1.8–2.5 K. Pre-heat treatment of the precursor films on CeO2/Y SZ/Y2O3/Ni/NiW substrates under an O2 atmosphere condition before the conversion resulted in smooth surfaces without large secondary phase particles embedded in the films.

There is interest in probing the feasibility and possible advantages of making uniform and cost-effective long-length coated conductors through a low-pressure processing approach. The low-pressure approach, eliminating the boundary layer and gas flow considerations, consumes much less of the processing gases and offers the possibility of improved uniformity and faster growth rate of superconducting films. Here, we have fabricated Y Ba2Cu3O7?? (YBCO) epitaxial films of thickness 0.1?1.0??m on SrTiO3 single crystal substrates using ex situ post-deposition processing of co-evaporated Y, BaF2 and Cu precursors in a controlled low-pressure gas mixture of oxygen and water vapour. Partial pressures of oxygen (PO2) and water vapour (PH2O) as low as 10 and 0.1?mTorr, respectively, were used. X-ray diffraction and scanning electron microscopy inspection were conducted for structure characterization of the films. High critical current densities (Jc) of at 77?K in self-field were obtained, yielding properties comparable to those of in situ films and ex situ films processed under atmospheric pressure condition.

Critical current density Jc in polycrystalline or granular superconducting material is known to be hysteretic with applied field H due to the focusing of field within the boundary between adjacent grains. This is of concern in the so-called coated conductors wherein superconducting film is grown on a granular, but textured surface of a metal substrate. While previous work has mainly been on Jc determined using induced or magnetization currents, the present work utilizes transport current via an applied potential in strip geometry. It is observed that the effect is not as pronounced using transport current, probably due to a large difference in criterion voltage between the two types of measurements. However, when the films are narrowed by patterning into 200-, 100-, or 80-micron, the hysteresis is clearly seen, because of the forcing of percolation across higher-angle grain boundaries. This effect is compared for films grown on ion-beam-assisted-deposited (IBAD) YSZ substrate and those grown on rolling-assisted-biaxially-textures substrates (RABiTS) which have grains that are about ten times larger. The hysteresis is more pronounced for the latter, which is more likely to have a weak grain boundary spanning the width of the microbridge. This is also of concern to applications in which coated conductors will be striated in order to reduce of AC losses., Comment: text-only: 10 pages, plus 5 figures on 5 pages