Irreversibility field and flux pinning in MgB₂with and without SiC additions

Abstract

Critical current density was measured at 4.2 K for MgB 2 strands with and without SiC additions. In some cases measurements were performed on longer (1 m) samples wound on barrels, and these were compared to magnetic measurements. Most measurements were performed on short samples at higher fields (up to 18 T). It was found that in-situ processed strands with 10% SiC additions HT at 700-800°C show improved H r and F p values as compared to control samples, with H r increasing by 1.5 T. At 900°C even larger improvements are seen, with H r reaching 18 T and F p values maximizing at 20 GN/m 3 .

Large upper critical field and irreversibility field in MgB2 wires with SiC additions

“…Ramp-up and ramp-down times were short. Transport J c results for similar wires have been previously reported, 11 val-ues for samples from Strand A of the present series gave 8 ϫ 10 4 A/cm 2 at 5 T and 4.2 K. Four-point transport measurements were made on 1 cm long samples at the National High Magnetic Field Laboratory in Tallahassee, Florida. Standard Pb-Sn solder was used for forming the contacts on the outer sheath, and the distance between the voltage taps was 5 mm.…”

“…2͒, and more generally high-field properties in wires with SiC. [7][8][9][10][11] Bulk samples which had been exposed to excess Mg vapor showed high B c2 values as well, with a B c2 ͑0͒ estimate of 29 T.…”

“…Hydride-based MgB 2 powder with SiC dopants was also investigated, and seen to give B c2 values of Ϸ23 T. 21 Dou et al [7][8][9][10] showed improved high-field critical current results for SiC, and similar wires measured in this laboratory showed improvements in the apparent irreversibility field as might be extrapolated from transport results. 11 In this work, strands of similar construction were investigated systematically, and high-field resistive transitions were used to demonstrate relatively large values of 0 H irr and B c2 with various kinds of SiC dopants under various heating conditions.…”

“…For strands A and B, the powders were mixed in a rotating V-shaped tube and then planetary milled. 11 Coarse SiC ͑200 nm͒ powders were added during this process in the proportion 10 mol % of SiC to 90 mol % of binary MgB 2 ͓͑MgB2͒0.9͑SiC͒0.1͔. Strands C and D, fabricated at the University of Wollongong, were also made from an in situ route, in this case with 10 wt % of "fine" SiC powder ͑15 and 30 nm͒.…”

The effect of doping level and sintering temperature on Jc(H) performance in nano-SiC doped and pure MgB2 wires

“…The exceptional properties of SiC as a dopant have been verified by a number of groups over the past few years. [7][8][9][10][11][12][13][14][15][16][17][18] However SiC doping was found to have some negative effect on J c in the low field region. The J c for SiC doped MgB 2 was lower than that for undoped MgB 2 below 4 T at 5 K and below 2.5 T at 20 K. 2,13,17 There are many applications in the low field region such as in open magnetic resonance imaging ͑MRI͒ transformers and electric cables which normally operate at around 1-3 T. Thus it is important that the enhancement of J c by SiC doping can be extended to include all the field regions.…”