Download N. Chikumoto

Effect of cation nonstoichiometry on the magnetic behavior of
cuprate superconductor
N. Chikumoto
Superconductivity Research Laboratory, International Superconductivity Technology Center,
1-10-13 Shinonome, Koto-ku, Tokyo, 135-0062, Japan
Numerous efforts have been made for the enhancement of the critical current density by
introducing effective pinning centers. Chemical doping is one of the best methods to introduce
pinning centers. Chong et al. [1] reported that the magnetic properties of Bi2Sr2CaCu2Oy (Bi2212)
compound are largely improved by a certain amount of Pb-substitution. Large critical current
densities observed in light rare earth (RE)Ba2Cu3Oy system is ascribed to the LRE-Ba substitution
[2].
Recently Eisaki et al. [3], pointed out that effect of chemical inhomogeneity differs
depending on its location relative to the CuO5 pyramids. In case of Bi2212 system, the Tc decreases
largely when Sr2+ site (A site) is replaced by Bi3+: Tc decreases from 94.0 K for stoichiometric
composition to 82.4 K for x = 0.2 in Bi2+xSr2-xCaCu2Oy.
On the other hand, effect of chemical
inhomogeneity in the Ca-site on Tc is very small. However, the relationship between magnetic
properties and substitution site is not yet studied.
In the present study, we present the effect of Sr-site cation nonstoichiometry on the magnetic
properties of Bi2212. By combining local magnetization measurement such as magneto-optical
imaging technique and Bitter decoration technique, with local chemical analysis using EPMA, we
investigated the relationship between magnetic behavior and chemical inhomogeneity. As for Sr-site
disorder, we observed the systematic enhancement of bulk pinning by reducing the
nonstoichiometry. The critical current density reached 2 x 106 A/cm2 at 20K, which is ever reported
on the present system.
Since the cation disorder in Sr-site is inherent in the present system, this
result suggests that its effect should be take into account to avoid misinterpretation of experimental
data.
This work has been carried out as a collaborative work with Mr. K. Furusawa, Mr. T. Muraoka, Dr.
S. Tajima, Dr. M. Murakami, and Dr. H. Eisaki. This work was supported by the New Energy and
Industrial Technology Development Organization (NEDO) as Collaborative Research and
Development of Fundamental Technologies for Superconductivity Applications
[1] I. Chong, et al., Science 276, 770 (1997).
[2] M. Murakami et al., Physica C 235-240, 2781 (1994)
[3] H. Eisaki, et al., Phys. Rev. B 69, 064512 (2004)
Corresponding author e-mail; [email protected]