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

G Pasquini,L Civale,G Serrano,A J Moreno,A Serquis

doi:10.1063/1.4813132

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.

Highlights

Since the discovery of the superconductor MgB2,1 a lot of work was devoted to understand and to improve its pinning properties
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

Summary

Introduction

Since the discovery of the superconductor MgB2,1 a lot of work was devoted to understand and to improve its pinning properties. Several groups have achieved a good improvement of the transport properties. Good results for increasing Jc have been achieved by chemical doping or by the inclusion of nonsuperconducting phases, in particular with carbon nanotubes (CNT) inclusions, with diameters close to the MgB2 coherence length n. In a previous publication we have reported results in samples with double wall CNTs additions showing both effects: an important increase in the critical current density and the upper critical field Hc2.7,8 it is not clear if this two effects are connected. Recent works have studied the activation energy in dirty MgB2 samples, but the results are not conclusive.. Recent works have studied the activation energy in dirty MgB2 samples, but the results are not conclusive. the vortex physics underlying this performance improvement has not been so far understood

Results

Discussion

Conclusion