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Vortex pinning in CNT-doped MgB2 superconductor

The magnetoresistance and critical current density, Jc, of undoped and doped with short multiwalled carbon nanotubes (SMW-CNT) MgB2 has been investigated in the temperature range 2-40 K and in magnetic field B ≤ 16T. The samples were Fe – sheathed wires and tapes annealed at 900o C and 1000o C, respectively [1]. Doping, by partial substitution of boron with carbon in MgB2 , decreases the superconducting transition temperature Tc , but increases upper critical field Hc2 probably due to effects of alloying on two-gap MgB2 superconductor [2]. Simultaneously, inhomogeneous doping and nanoprecipitates formed during annealing enhance the pinning of vortices in doped samples. This shows up in enhanced pinning potential U0(B), irreversibility field Birr(T), Jc(B) and volume pinning force Fp = JcB, especialy at elevated fields B. Unfortunately, the magnitude of Jc of present wires and tapes is limited by the core porosity (  50 %) and an inhomogenous distribution of CNTs within the core. [1] J. H. Kim, W. K. Yeah, M. J. Quin, X. Xu and S. X. Dou, Journal of Applied Physics, 100 (2006) 013908 ; [2] A. Gurevich, Physical Review B, 67 (2003) 184515.

superconductivity; MgB2; carbon nanotubes

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