TY - JOUR
T1 - Nano Fe 3O 4 induced fluxoid jumps and low field enhanced critical current density in MgB 2 superconductor
AU - Singh, K. P.
AU - Awana, V. P.S.
AU - Balamurugan, S.
AU - Shahabuddin, M.
AU - Singh, H. K.
AU - Husain, M.
AU - Kishan, H.
AU - Bauminger, E. R.
AU - Felner, I.
PY - 2008/1
Y1 - 2008/1
N2 - Nano particle of Fe 3O 4 (nFe 3O 4) up to 6 at% were doped in the superconducting MgB 2 samples. Despite the strong ferromagnetic nature of Fe 3O 4, both the ac susceptibility and the resistivity measurements show that up to 4 at% of Fe 3O 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 3O 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 and 20 K) indicating an enhanced flux pinning and the magnetic activation, i.e., the interaction between the magnetic dipole of Fe ion and the vortices is weak in comparison to the effective pinning potential. Whereas, at 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% nFe 3O 4 only. Magnetization plots of higher Fe content samples exhibited clear paramagnetic background. Mossbauer measurements for the higher (4, 6 at%) nFe 3O 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 nFe 3O 4 particles decompose and form possibly an intermetallic Fe-B phase in the matrix.
AB - Nano particle of Fe 3O 4 (nFe 3O 4) up to 6 at% were doped in the superconducting MgB 2 samples. Despite the strong ferromagnetic nature of Fe 3O 4, both the ac susceptibility and the resistivity measurements show that up to 4 at% of Fe 3O 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 3O 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 and 20 K) indicating an enhanced flux pinning and the magnetic activation, i.e., the interaction between the magnetic dipole of Fe ion and the vortices is weak in comparison to the effective pinning potential. Whereas, at 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% nFe 3O 4 only. Magnetization plots of higher Fe content samples exhibited clear paramagnetic background. Mossbauer measurements for the higher (4, 6 at%) nFe 3O 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 nFe 3O 4 particles decompose and form possibly an intermetallic Fe-B phase in the matrix.
KW - Critical current density
KW - MgB
KW - Nano-Fe O
KW - Vacuum synthesis
UR - http://www.scopus.com/inward/record.url?scp=37549040176&partnerID=8YFLogxK
U2 - 10.1007/s10948-007-0294-8
DO - 10.1007/s10948-007-0294-8
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AN - SCOPUS:37549040176
SN - 1557-1939
VL - 21
SP - 39
EP - 44
JO - Journal of Superconductivity and Novel Magnetism
JF - Journal of Superconductivity and Novel Magnetism
IS - 1
ER -