A comprehensive study of the pinning mechanisms of MgB sub(2) wires treated with malic acid and their relationships with lattice defects

• Published in: Superconductor science & technology 2013-01, Vol.26 (8), p.1-6
• Main Authors: Motaman, A, Hossain, M S A, Xu, X, See, K W, Chung, K C, Dou, S X
• Format: Article
• Language: English
• Subjects: Borides; Critical temperature; Flux pinning; Magnesium compounds; Malic acid; Mean free path; Pinning; Sintering; Wire
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/0953-2048/26/8/085013

The effects of sintering temperature on the lattice parameters, structural strain, critical temperature (T sub(c)), critical current density (J sub(c)), irreversibility field (B sub(irr)), upper critical field (B sub(c2), and resistivity ([psi]) of MgB sub(2) wires treated with 10 wt.% malic acid (C sub(4)H sub(6)O sub(5)) are investigated in this paper. The a-lattice parameter of the sample treated with malic acid was drastically reduced, to 3.0745 A, as compared to those for the undoped samples. Reduction in the a-lattice parameter is related to crystalline imperfections arising from carbon substitution-as confirmed by x-ray diffraction and Raman spectra-which play a vital role in enhancing J sub(c), B sub(c2) and B sub(irr). We have also analyzed the pinning mechanisms, and concluded that flux pinning is dominated by point and correlated pinning at lower and higher magnetic fields, respectively, for the carbon-doped samples sintered at both 700 and 900 [degrees]C. The degree of flux pinning enhancement and the ratio RHH (B sub(c2)/B sub(irr)) have been estimated to guide us towards further enhancement of J sub(c). We argue that delta l and [deta]T sub(c) pinning mechanisms, based on variation of the mean free path (l) and the critical temperature, respectively, coexist in the MgB sub(2) wires treated with malic acid, regardless of the sintering temperature. The delta l pinning is predominant at lower operating temperatures, and delta T sub(c) pinning starts close to T sub(c), which means that spatial variation in the charge carrier mean free path is the main mechanism responsible for the flux pinning in the MgB sub(2) wires treated with malic acid that were sintered at 700 and 900 [degrees]C.