Carbon nanotubes effects on the relaxation properties and critical current densities of MgB2 superconductor

Abstract

Addition of nonsuperconducting phases, such as carbon nanotubes, can modify the superconducting properties of MgB2 samples, improving the critical current density and upper critical field. A full understanding of the flux creep mechanism involved is crucial to the development of superconducting magnets in persistent mode, one of the main thrusts for the development of MgB2 wires. In this paper we present a creep study in bulk MgB2 samples, pure and with different amounts of carbon nanotubes additions. We conclude that the most consistent picture at low temperatures is a single vortex pinning regime, where the correlation length is limited by the grain size. We introduce a novel analysis that allows us to identify the region where the Anderson-Kim model is valid