The effect of heat-treatment temperature on the superconducting properties of malic acid-doped MgB2/Fe wire

The effects of the heat-treatment temperature on the carbon (C) substitution amount, full width at half-maximum (FWHM) value, critical temperature (T-c), critical current density (J(c)), irreversibility field (H-irr) and upper critical field (H-c2) have been investigated for 10 wt% malic acid-doped MgB2/Fe wires. All the samples were fabricated by the in situ powder-in-tube ( PIT) method and heat- treated within a temperature range of 650-1000 degrees C. As the heat- treatment temperature increased, it seemed that the lattice distortion was increased by a more active C substitution into the boron ( B) sites from the malic acid addition. These increased electron scattering defects seemed to enhance the J(c)-H properties in spite of an improvement in the crystallinity, such as a decrease of the FWHM value and an increase of the T-c. Compared to the un-doped wire heat- treated at 650 degrees C for 30 min, the J(c), H-c2 and H-irr were enhanced by the C doping in a high-field regime. The wire heat- treated at 900 degrees C resulted in a higher magnetic J(c) of approximately 10(4) A cm(-2) at 5 K and 8 T, and it showed a H-irr value of 11 T at 20 K from the resistance (R) versus temperature (T) curves.