Nano Fe3O4 Induced Fluxoid Jumps and Low Field Enhanced Critical Current Density in MgB2 Superconductor

• Published in: Journal of superconductivity 2008, Vol.21 (1), p.39-44
• Main Authors: Singh, K. P., Awana, V. P. S., Balamurugan, S., Shahabuddin, M., Singh, H. K., Husain, M., Kishan, H., Bauminger, E. R., Felner, I.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Critical currents; Exact sciences and technology; Magnetic Materials; Magnetism; Physics; Physics and Astronomy; Properties of type I and type II superconductors; Strongly Correlated Systems; Superconductivity; Vortex lattices ,flux pinning, flux creep
• ISSN: 1557-1939; 0896-1107; 1557-1947
• DOI: 10.1007/s10948-007-0294-8

Nano particle of Fe 3 O 4 ( n Fe 3 O 4 ) up to 6 at% were doped in the superconducting MgB 2 samples. Despite the strong ferromagnetic nature of Fe 3 O 4 , both the ac susceptibility and the resistivity measurements show that up to 4 at% of Fe 3 O 4 , T c =38 K is not changed, whereas for 6% T c decreases by 6 K. This indicates that a low concentration of Fe does not substitute either the Mg or B sites and probably occupies the intergrain spaces. For 0.5% doped Fe 3 O 4 , an increase in J c with respect to the pure MgB 2 samples is observed in the lower field and temperature regions ( H 2 T, J c of the doped samples is always less than that of MgB 2 , and the activation is dominant in comparison with the effective pinning potential provided by the doping. Flux jumps are observed in lower T and H regions for the samples doped up to 1% n Fe 3 O 4 only. Magnetization plots of higher Fe content samples exhibited clear paramagnetic background. Mossbauer measurements for the higher (4, 6 at%) n Fe 3 O 4 doped MgB 2 samples show that at RT, the hyperfine field for both samples is ∼100 kOe and ∼120 kOe at 90 K. This means that the n Fe 3 O 4 particles decompose and form possibly an intermetallic Fe-B phase in the matrix.