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There exist two kinds of critical current densities in polycrystalline bulk of MgB2, i.e., the large local critical current density corresponding to the shielding current in inductive measurements, which flows inside the grains, and the small global critical current density that flows through the grains for whole sample. This behavior is considered to be mainly caused by the significant granularity in polycrystalline bulk. In this work, MgB2 superconductors are prepared under different Spark plasma sintering (SPS) heating rates. The microstructures of the samples are investigated, and their critical current densities are measured by Campbell method from the penetrating AC flux profile and the AC magnetic field versus penetration depth. It is found that an extremely high global critical current flows through the whole sample with a bigger grain size, which is prepared by a low heating rate during SPS sintering. That is to say, the grain refinement only increases the local critical current density of the sample. These results imply that the global current is reduced due to the existence of various defects and the poor electrical connectivity in MgB2 sample.
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Keywords:
- grain refinement /
- Campbell method /
- MgB2 superconductor /
- local critical current density and global critical current density
[1] Source W 2011 Superconductivity, BCS Theory, John Bardeen, Meissner Effect, Technological Applications of Superconductivity (Washington DC: Original Publisher) pp11–23
[2] Government U S 2011 High Temperature Superconductivity in Perspective (Washington DC: Original Publisher) pp81–93
[3] Thomas M L, Beena K, Hyunsoo K 2012 Physica C 483 91
[4] Muller K H, Andrikidis C, Liu H K 1994 Phys. Rev. B 50 10218
[5] Teruo M 2007 Flux Pinning in Superconductors (Berlin: Springer-Verlag) pp221–350
[6] Baorong N, Zhiyong L, Yoshihiro M 2008 Physics C 468 1443
[7] Guo Z C, Suo H L, Liu Z Y, Liu M, Ma L 2012 Acta Phys. Sin. 61 177401 (in Chinese) [郭志超, 索红莉, 刘志勇, 刘敏, 马麟 2012 物理学报 61 177401]
[8] Otabe E S, Kiuchi M, Kawai S 2009 Physica C 469 1940
[9] Ni B, Ge J, Yuri T, Edmund S O 2011 IEEE Trans. Appl. Supercond. 21 2862
[10] Ma Z, Liu Y, Cai Q 2012 Nanoscale 4 2060
[11] Kovac P, Husek I, Kulich M 2010 Physica C 470 340
[12] Malagoli A, Braccini V, Bernini C 2010 Supercond. Sci. Technol. 23 2
[13] Takahashi M, Okada M, Nakane T 2009 Supercond. Sci. Technol. 22 12
[14] Kim D H, Hwang T J, Cha Y J 2009 Physica C 469 1059
[15] Ahn J H, Oh S 2009 Physica C 469 1235
[16] Aldica G, Batalu D, Popa S 2012 Physica C 477 43
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[1] Source W 2011 Superconductivity, BCS Theory, John Bardeen, Meissner Effect, Technological Applications of Superconductivity (Washington DC: Original Publisher) pp11–23
[2] Government U S 2011 High Temperature Superconductivity in Perspective (Washington DC: Original Publisher) pp81–93
[3] Thomas M L, Beena K, Hyunsoo K 2012 Physica C 483 91
[4] Muller K H, Andrikidis C, Liu H K 1994 Phys. Rev. B 50 10218
[5] Teruo M 2007 Flux Pinning in Superconductors (Berlin: Springer-Verlag) pp221–350
[6] Baorong N, Zhiyong L, Yoshihiro M 2008 Physics C 468 1443
[7] Guo Z C, Suo H L, Liu Z Y, Liu M, Ma L 2012 Acta Phys. Sin. 61 177401 (in Chinese) [郭志超, 索红莉, 刘志勇, 刘敏, 马麟 2012 物理学报 61 177401]
[8] Otabe E S, Kiuchi M, Kawai S 2009 Physica C 469 1940
[9] Ni B, Ge J, Yuri T, Edmund S O 2011 IEEE Trans. Appl. Supercond. 21 2862
[10] Ma Z, Liu Y, Cai Q 2012 Nanoscale 4 2060
[11] Kovac P, Husek I, Kulich M 2010 Physica C 470 340
[12] Malagoli A, Braccini V, Bernini C 2010 Supercond. Sci. Technol. 23 2
[13] Takahashi M, Okada M, Nakane T 2009 Supercond. Sci. Technol. 22 12
[14] Kim D H, Hwang T J, Cha Y J 2009 Physica C 469 1059
[15] Ahn J H, Oh S 2009 Physica C 469 1235
[16] Aldica G, Batalu D, Popa S 2012 Physica C 477 43
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