Superconducting properties of (M x /YBa 2Cu 3O 7-δy ) N multilayer films with variable layer thickness x

T. J. Haugan, P. N. Barnes, T. A. Campbell, N. A. Pierce, F. J. Baca, M. F. Locke, I. Brockman, A. L. Westerfield, J. M. Evans, R. Morgan, P. Klenk, B. C. Harrison, A. D. Chaney, I. Maartense

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3 Scopus citations

Abstract

The superconducting properties of (M x /YBa 2Cu 3O 7-δy ) N multilayer films were studied for varying layer thickness x. Different M phases were examined including green-phase Y 2BaCuO 5 (211), Y 2O 3, BaZrO 3, CeO 2, SmBa 2Cu 3O 7-δ (Sm123), brown-phase La 2BaCuO 5 (La211), and MgO. Multilayer (M x /YBa 2 Cu 3O 7-δy ) N structures were grown by pulsed laser deposition onto SrTiO 3 or LaAlO 3 single-crystal substrates by alternate ablation of separate YBa 2Cu 3O 7-δ (123) and M targets, at temperatures of 750°C to 790°C. The x layer thickness was varied from 0.1 nm to 4.5 nm, and the y 123 layer thickness was kept constant within a given range of 10 to 25 nm. Different M phase and x layer thicknesses caused large variations of the microstructural and superconducting properties, including superconducting transition (T c), critical current density as a function of applied magnetic field J c(H), self-field J c(77 K), and nanoparticle layer coverage. Strong flux-pinning enhancement up to 1 to 3x was observed to occur for M additions of 211 and BaZrO 3 at 65 to 77 K, Y 2O 3 at 65 K, and CeO 2 for H < 0.5 T. BaZrO 3 had a noticeably different epitaxy forming smaller size nanoparticles ∼ 8 nm with 3 to 4x higher areal surface particle densities than other M phases, reaching 5 × 10 11 nanoparticles cm -2. To optimize flux pinning and J c (65 to 77 K, H = 2 to 3 T), the M layer thickness had to be reduced below a critical value that correlated with a nanoparticle surface coverage <15% by area. Unusual effects were observed for poor pinning materials including Sm123 and La211, where properties such as self-field J c unexpectedly increased with increasing x layer thickness.

Original languageEnglish (US)
Pages (from-to)1234-1242
Number of pages9
JournalJournal of Electronic Materials
Volume36
Issue number10
DOIs
StatePublished - Oct 2007

Bibliographical note

Funding Information:
The authors would like to express appreciation to Lyle Brunke, John Murphy, Joe Kell, and David Blubaugh for assistance with Jc(H,T,θ) and film thickness measurements. The authors are also grateful for support of this work by the U.S. Air Force Office of Scientific Research and the Air Force Research Laboratory—Propulsion Directorate.

Keywords

  • Critical current density
  • Flux pinning
  • Magnetic field
  • Multilayer
  • Nanoparticle
  • Pulsed laser deposition
  • Superconductor
  • Thin film
  • YBa Cu O

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