Correlated Enhancement of Hc 2 and Jc in Carbon Nanotube Doped MgB 2

1. B a r I l o c h e Correlated Enhancement of Hc2 and Jc in Carbon Nanotube Doped MgB2 A. Serquis et al. achieved the enhancement of current-carrying performance and critical magnetic field simultaneously in polycrystalline MgB2 by doping it with double-wall carbon nanotube. The optimum content, from the point of view of the critical current density Jc, is in the range 2.5-10 at.% depending on field and temperature. Record values of the upper critical field, Hc2(4 K) = 41.9 T (Hc2(0)  44.4 T), were reached by Serquis et al. in a bulk sample with 10 at.% nominal content. The results are successfully described using a theoretical model for a two-gap superconductor in the dirty limit first proposed by Gurevich (A.Gurevich et al., Supercond. Sci. Technol. 17, 278 (2004)). . B: Hc2 versus reduced temperature t for CNT00, CNT01 and CNT10 samples and the fit to data using the expresion proposed by Gurevich et al. Inset: A typical TEM image of a DWCNT with a 3 nm diameter is displayed in the lower inset (arrows indicate the walls of the double wall nanotube) . A: Jc vs magnetic field determined from magnetization measurements for samples CNT00 (MgB2 pure), CNT25 (2.5% doping), CNT10 (10% doping) and CNT125 (12.5 % doping), at T = 5 K (solid symbols) and 20 K (open symbols). The inset illustrates Jc as function of x at m0H = 4 T . A. Serquis. G. Serrano, S.M. Moreno, L. Civale, B. Maiorov, F. Balakirev and M. Jaime Superconductor Science & Technology 20, L12 (2007).