Gupta, Anurag and Kumar, Anuj and Narlikar, A. V. (2009) Normal state connectivity and Jc of weakly coupled MgB2 particles. Superconductor Science and Technology , 22 (10). 105005-1-105005-10. ISSN 0953-2048

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A series of ex situ samples of bulk MgB2 were prepared with an addition of excess Mg up to 5% and varying sintering temperatures between 700 and 950 °C. All the samples were subjected to XRD and SEM characterization as well as thermoelectric power S(T), resistivity ρ(T) and magnetization M(B) measurements at 4.2 and 20 K and applied fields B = 0–8 T. Various normal and superconducting state properties show weakly coupled particles in the samples. The samples typically show high values of ρ(300 K) that vary between 0.12 and 254 mΩ cm. The critical current density Jc(4.2 K,1 T) show low values that vary between 1.8 × 107 and 1.7 × 108 A m−2. The temperature dependence of resistivity in the normal state scales perfectly among the samples to within a multiplication factor. Following Rowell's analysis (2003 Supercond. Sci. Technol. 16 R17), this indicates a difference in normal state connectivity, i.e. effective current-carrying cross section, AF, which is found to vary from 0.02% to 7% in different samples. Surprisingly, no correlation between the Jc and AF is found in our samples. However, Jc(B) of all the samples can be scaled within a multiplication factor at both 4.2 and 20 K until crossover fields Bcr~2 and 1.3 T, respectively. The Jc(B) of the samples follows a B−1 dependence until Bcr, at both T = 4.2 and 20 K, beyond which it decreases rapidly towards zero with increasing B. The superconducting transition measured resistively in the presence of B shows an enhanced broadening. We further attempt to delineate the role of the intra-particle and inter-particle regions in determining the Jc(B) and ρ(T,B) properties of our weakly coupled samples.

Item Type: Article
Additional Information: Copyright for this article belongs to M/s Institute of Physics.
Subjects: Physics
Depositing User: Ms Neetu Chandra
Date Deposited: 20 Sep 2012 13:01
Last Modified: 20 Sep 2012 13:01

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