Vortex dynamics in superconducting MgB2 and prospects for applications

Abstract

The recently discovered superconductor magnesium diboride, MgB2, has a transition temperature, Tc, approaching 40 K, placing it intermediate between the families of low- and high-temperature superconductors. In practical applications, superconductors are permeated by quantized vortices of magnetic flux. When a supercurrent flows, there is dissipation of energy unless these vortices are 'pinned' in some way, and so inhibited from moving under the influence of the Lorentz force. Such vortex motion ultimately determines the critical current density, Jc, which the superconductor can support. Vortex behaviour has proved to be more complicated in high-temperature superconductors than in low-temperature superconductors and, although this has stimulated extensive theoretical and experimental research, it has also impeded applications. Here we describe the vortex behaviour in MgB2, as reflected in Jc and in the vortex creep rate, S, the latter being a measure of how fast the 'persistent' supercurrents decay. Our results show that naturally occurring grain boundaries are highly transparent to supercurrents, a desirable property which contrasts with the behaviour of the high-temperature superconductors. On the other hand, we observe a steep, practically deleterious decline in Jc with increasing magnetic field, which is likely to reflect the high degree of crystalline perfection in our samples, and hence a low vortex pinning energy.

Magnetization and microwave study of superconductingMgB2

“…The temperature dependence of H irr has also been investigated [31][32][33][34]. For example, two reports of the magnetic irreversibility field have found that H irr scales linearly with the temperature deviation from T c [31,32] but the analysis of H irr reported in two other studies gives a scaling of the form…”

Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi

“…Two important ways to increase critical current density are by the enhancement of the pinning force 30,31 and/or by increasing the crosssectional area fraction. 7 First, we consider the area fraction.…”

Carbohydrate doping to enhance electromagnetic properties of MgB2 superconductors

“…[2][3][4][5][6] To take advantage of its T c of 39 K, enhancements of both the upper critical field ͑H c2 ͒ and J c are essential. Attempts to accomplish this have invoked the introduction of numerous techniques including chemical doping, [2][3][4][5][6] irradiation, 7 and various thermomechanical processing techniques. 8,9 Chemical doping is a simple and readily scalable technique.…”