skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Relationship between flux pinning and microstructure in MgB{sub 2} thin films with columnar grains formed by molecular beam epitaxy

Abstract

The relationship between flux pinning and microstructure in MgB{sub 2} thin films with columnar grains was investigated. Two kinds of as-grown MgB{sub 2} thin films were prepared with or without inclination of columnar grain growth with respect to the substrate plane by using molecular beam epitaxy. In a magnetic field, maximum J{sub c} was obtained when the field angle matched the direction of columnar grain growth. The fabricated MgB{sub 2} thin films showed a high critical current density of J{sub c}=1.3x10{sup 5} A/cm{sup 2} in 14 T at 4.2 K. The present results give a direct proof of flux pinning originating in columnar grain boundaries for MgB{sub 2} thin films.

Authors:
; ; ; ;  [1];  [2];  [2]
  1. Advanced Research Laboratory, Hitachi Ltd., 1-280, Higashi-Koigakubo, Kokubunji-shi, Tokyo 185-8601 (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
20960196
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 14; Other Information: DOI: 10.1063/1.2720272; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRITICAL CURRENT; CRYSTAL GROWTH; CURRENT DENSITY; GRAIN BOUNDARIES; GRAIN GROWTH; LAYERS; MAGNESIUM BORIDES; MAGNETIC FIELDS; MAGNETIC FLUX; MOLECULAR BEAM EPITAXY; SUBSTRATES; SUPERCONDUCTIVITY; SUPERCONDUCTORS; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0000-0013 K; THIN FILMS; TRANSMISSION ELECTRON MICROSCOPY

Citation Formats

Yamamoto, H., Tsukamoto, A., Saitoh, K., Okada, M., Kitaguchi, H., Material Research Laboratory, Hitachi Ltd., 7-1-1, Omika-cho, Hitachi-shi, Ibaraki-ken 319-1292, and National Institute for Materials Science, 1-2-1, Sengen, Tsukuba 305-0047. Relationship between flux pinning and microstructure in MgB{sub 2} thin films with columnar grains formed by molecular beam epitaxy. United States: N. p., 2007. Web. doi:10.1063/1.2720272.
Yamamoto, H., Tsukamoto, A., Saitoh, K., Okada, M., Kitaguchi, H., Material Research Laboratory, Hitachi Ltd., 7-1-1, Omika-cho, Hitachi-shi, Ibaraki-ken 319-1292, & National Institute for Materials Science, 1-2-1, Sengen, Tsukuba 305-0047. Relationship between flux pinning and microstructure in MgB{sub 2} thin films with columnar grains formed by molecular beam epitaxy. United States. doi:10.1063/1.2720272.
Yamamoto, H., Tsukamoto, A., Saitoh, K., Okada, M., Kitaguchi, H., Material Research Laboratory, Hitachi Ltd., 7-1-1, Omika-cho, Hitachi-shi, Ibaraki-ken 319-1292, and National Institute for Materials Science, 1-2-1, Sengen, Tsukuba 305-0047. Mon . "Relationship between flux pinning and microstructure in MgB{sub 2} thin films with columnar grains formed by molecular beam epitaxy". United States. doi:10.1063/1.2720272.
@article{osti_20960196,
title = {Relationship between flux pinning and microstructure in MgB{sub 2} thin films with columnar grains formed by molecular beam epitaxy},
author = {Yamamoto, H. and Tsukamoto, A. and Saitoh, K. and Okada, M. and Kitaguchi, H. and Material Research Laboratory, Hitachi Ltd., 7-1-1, Omika-cho, Hitachi-shi, Ibaraki-ken 319-1292 and National Institute for Materials Science, 1-2-1, Sengen, Tsukuba 305-0047},
abstractNote = {The relationship between flux pinning and microstructure in MgB{sub 2} thin films with columnar grains was investigated. Two kinds of as-grown MgB{sub 2} thin films were prepared with or without inclination of columnar grain growth with respect to the substrate plane by using molecular beam epitaxy. In a magnetic field, maximum J{sub c} was obtained when the field angle matched the direction of columnar grain growth. The fabricated MgB{sub 2} thin films showed a high critical current density of J{sub c}=1.3x10{sup 5} A/cm{sup 2} in 14 T at 4.2 K. The present results give a direct proof of flux pinning originating in columnar grain boundaries for MgB{sub 2} thin films.},
doi = {10.1063/1.2720272},
journal = {Applied Physics Letters},
number = 14,
volume = 90,
place = {United States},
year = {Mon Apr 02 00:00:00 EDT 2007},
month = {Mon Apr 02 00:00:00 EDT 2007}
}
  • We report significant enhancement in the flux-pinning of epitaxial NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (NdBCO) films on rolling-assisted biaxially textured substrates (RABiTS) via the incorporation of a two-dimensional array of columnar defects comprised of self-assembled BaZrO3 (BZO) nanodots. Pure NdBCO films and NdBCO films incorporating BZO nanodots, both with the same thickness of 0.6 {micro}m, were epitaxially grown on RABiTS by pulsed laser deposition. A very dense and homogeneous distribution of BZO nanodot columns with typical intercolumn spacing of around 15-20 nm oriented along the c-axis of the film was observed in the NdBCO+BZO film. Compared to the pure NBCO filmmore » on RABiTS, the NdBCO+BZO film on RABiTS has an in-field critical current density (J{sub c}) of a factor of more than 2 in 0.1-1.5 T and a smaller power-law exponent {alpha}{approx}0.21 in the field regime where J{sub c}{approx}H{sup -{alpha}}.« less
  • 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, nearlymore » continuous vortex pins along the c-axis in YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO), in the form of self-assembled stacks of BaZrO{sub 3} (BZO) nanodots and nanorods. The nanodots and nanorods have a diameter of {approx}2-3 nm and an areal density ('matching field') of 8-10 T for 2 vol.% incorporation of BaZrO{sub 3}. 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, J{sub c}, varies as J{sub c} {approx}H{sup -{alpha}}, with {alpha} {approx} 0.3 rather than the usual values 0.5-0.65. Similar results were also obtained for CaZrO{sub 3} (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.« less
  • We have investigated the pinning of vortices in high-J{sub c} films of polycrystalline MgB{sub 2}, by studying the dependence of current density J on electric field E using both magnetic and transport methods. Precursor films of amorphous boron, deposited on sapphire substrates, were converted to 0.6 {mu}m thick MgB{sub 2} by post-annealing in the presence of Mg vapour at 890 {sup o}C for 1 h. In magnetic studies, a SQUID magnetometer was used conventionally to determine the induced current density by the Bean model. The decay of J with time t was determined unconventionally with the sample fixed in position,more » by monitoring the SQUID feedback voltage {proportional_to} J versus time. The logarithmic decay rate S = -d ln(J)/d ln(t) was found to be very low in the H-T phase space away from the irreversibility line. Complementary four-probe transport studies of E(J) were analysed as a power law dependence of the form E {proportional_to} J{sup {pi}} and used to obtain the corresponding creep rate S = 1/(n-1). Effective values for n approach and often significantly exceed 100. From these results, we estimate the effective energy U{sub 0} for vortex pinning, as a function of magnetizing field H.« less