Enhanced upper critical field in Co-doped Ba122 superconductors by lattice defect tuning

Nanoscale defects in superconductors play a dominant role in enhancing superconducting properties through electron scattering, modulation of coherence length, and correlation with quantized magnetic flux. For iron-based superconductors (IBSCs) that are expected to be employed in high-field magnetic...

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Veröffentlicht in:APL materials 2019-11, Vol.7 (11), p.111107-111107-6
Hauptverfasser: Tokuta, Shinnosuke, Yamamoto, Akiyasu
Format: Artikel
Sprache:eng
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Zusammenfassung:Nanoscale defects in superconductors play a dominant role in enhancing superconducting properties through electron scattering, modulation of coherence length, and correlation with quantized magnetic flux. For iron-based superconductors (IBSCs) that are expected to be employed in high-field magnetic applications, a fundamental question is whether such defects develop an upper critical field (Hc2) similar to that of conventional BCS-type superconductors. Herein, we report the first demonstration of a significantly improved Hc2 in a 122-phase IBSC by introducing defects through high-energy milling. Co-doped Ba122 polycrystalline bulk samples [Ba(Fe, Co)2As2] were prepared by sintering powder which was partially mechanically alloyed through high-energy milling. A remarkable increase in the full-width at half maximum of X-ray powder diffraction peaks, anomalous shrinkage in the a-axis, and elongation in the c-axis were observed. When lattice defects are introduced into the grains, the semiconductor behavior of the electric resistivity at a low temperature (T < 100 K), a slight decrease in transition temperature (Tc), an upturn of Hc2(T) near Tc, and a large increase in the Hc2(T) slope were observed. The slope of Hc2(T) increased approximately by 50%, i.e., from 4 to 6 T/K, and exceeded that of single crystals and thin films. Defect engineering through high-energy milling is expected to facilitate new methods for the designing and tuning of Hc2 in 122-phase IBSCs.
ISSN:2166-532X
2166-532X
DOI:10.1063/1.5098057