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In this paper we have investigated the effects of sintering time and temperature on the formation and critical current densities of Fe-clad MgB2 wires. MgB2 wires were fabricated using the powder-in-tube process and sintered for different periods of time at predetermined temperatures. All the samples were examined using XRD, SEM and magnetisation measurements. In contrast to the common practice of sintering for several hours, the present results show that there is no need for prolonged heat treatment in the fabrication of Fe-clad MgB2 wires. A total time in the furnace of several minutes is more than enough to form nearly pure MgB2 with high performance characteristics. The results from Tc, Jc and Hirr show convincingly that the samples which were sintered for 3 minutes above 800 oC are as good as those sintered for longer times. In fact, the Jc field performance for the most rapidly sintered sample is slightly better than for all other samples. Jc of 4.5 times 10 ^5 A/cm2 in zero field and above 10 ^5 A/cm2 in 2T at 15 K has been achieved for the best Fe-clad MgB2 wires. As a result of such a short sintering there is no need for using high purity argon protection and it is possible to carry out the heat treatment in a much less protective atmosphere or in air. These findings substantially simplify the fabrication process, making it possible to have a continuous process for fabrication and reducing the costs for large-scale production of MgB2 wires.Comment: 15 pages, one table, 9 figures, submitted to Physica C on June 8, 200

In this letter, we report the results of field (H) and temperature (T) dependent magnetization (M) measurements of a pellet of uniform, large-grain sintered MgB 2 . We show that at low temperatures the size of the pellet and its critical current density, J c (H) --i.e. its M(H) --ensure low field flux jumping, which of course ceases when M(H) drops below a critical value. With further increase of H and T the individual grains decouple and the M(H) loops drop to lower lying branches, unresolved in the usual full M(H) representation. After taking into account the sample size and grain size, respectively, the bulk sample and the grains were deduced to exhibit the same magnetically determined J c s (e.g. 10 5 A/cm 2 , 20 K, 0T) and hence that for each temperature of measurement J c (H) decreased monotonically with H over the entire field range, except for a gap within the grain-decoupling zone.

We demonstrate topological insulator (Bi 2 Te 3 ) dc SQUIDs, based on superconducting Nb leads coupled to nano-fabricated Nb-Bi 2 Te 3 -Nb Josephson junctions. The high reproducibility and controllability of the fabrication process allows the creation of dc SQUIDs with parameters that are in agreement with design values. Clear critical current modulation of both the junctions and the SQUID with applied magnetic fields have been observed. We show that the SQUIDs have a periodicity in the voltage-flux characteristic of Φ 0 , of relevance to the ongoing pursuit of realizing interferometers for the detection of Majorana fermions in superconductor-topological insulator structures.

Abstract-The nano-SiC doped MgB 2 /Fe wires were fabricated using a powder-in-tube method and an in-situ reaction process. The depression of with increasing SiC doping level remained rather small due to the counterbalanced effect of Si and C co-doping. The high level SiC co-doping allowed creation of the intra-grain defects and nano-inclusions, which act as effective pinning centers, resulting in a substantial enhancement in the ( ) performance. The transport for all the wires is comparable to the magnetic at higher fields despite the low density of the samples and percolative nature of current. The transport for the 10wt% SiC doped MgB 2 /Fe reached 660A at 5K and 4.5T ( = 133 000A/cm 2 ) and 540A at 20K and 2T ( = 108 000A/cm 2 ). The transport for the 10wt% SiC doped MgB 2 wire is more than an order of magnitude higher than for the state-the-art Fe-sheathed MgB 2 wire reported to date at 5K and 10T and 20K and 5T respectively. There is a plenty of room for further improvement in as the density of the current samples is only 50%.