High critical current density and enhanced irreversibility field in superconducting MgB2 thin films

Abstract

The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7 T at liquid helium temperature (4.2 K), significantly lower than about 10 T for Nb-Ti (ref. 6) and approximately 20 T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2 K greater than 14 T. In addition, very high critical current densities at 4.2 K are achieved: 1 MA cm-2 at 1 T and 105 A cm-2 at 10 T. These results demonstrate that MgB2 has potential for high-field superconducting applications.

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

“…17,18 Carbohydrates easily decompose at, or even below 650 1C, the melting temperature of magnesium, which enables low sintering temperature fabrication to suppress grain growth. Smaller grains are related to larger pinning force and higher critical current, [19][20][21][22] according to grain boundary pinning models. It is also claimed that more homogeneous mixing is possible than with other doping methods.…”

Fabrication and transport critical currents of multifilamentary MgB2/Fe wires and tapes

“…Soon after its discovery, several research groups have tried to demonstrate the feasibility of fabrication of MgB 2 wires or tapes with high critical current density using the Powder-In-Tube (PIT) method [6][7][8][9][10][11]. Large critical current densities of 10 6 A/cm 2 and significant enhancement of irreversibility line and H c2 have been reported in MgB 2 films grown on single-crystalline substrates [12][13]. These results brought further excitement to the development of MgB 2 in view of an eventual industrial application.…”

Correlated vortex pinning in Si-nanoparticle doped MgB2

“…Several techniques, such as alloying [11,12,13], particle irradiation [14,15,16,17] and mechanical processing [9,18] have been employed in order to improve the flux-pinning in MgB 2 , but with limited success. In particular, proton irradiation [14] increased B irr at 20 K, but also suppressed low-field J c , whereas alloying seems to enhance J c , but has little effect on B irr [12,13].…”