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Low-temperature sintering to fabricate MgB2 is considered a promising method because it reduces the formation of MgO and reduces the grain size, thereby increasing the critical current density. Chemical doping, ball milling of precursor and modifying the Mg source in precursor for low-temperature sintering have all been carefully investigated. However, the threshold of sintering temperature have been kept near 500 °C. A new in-situ method to low-temperature sintering using Mg(BH4)2 as a precursor is presented in this paper. Mg(BH4)2 decomposes into highly reactive nanoscale Mg and B in a molar ratio of 1:2 without impurities. In this method, only 2 h of sintering at 400 °C is required to completely react Mg with B to produce MgB2, and after 54 h sintering, the sample has comparable J C to the normal MgB2 from solid-state reaction method sintered at 800 °C. The sample sintered at 500 °C give better J C than normal MgB2 under both high and low magnetic field.

We theoretically investigate the spontaneous magnetization in double-junction and multi-junction π rings when the junctions' superconducting critical currents are not equal. The analytical solutions for the relations between the total magnetic flux Φ and the external magnetic flux Φx, the free energy f and the circulating current i, and the spontaneous magnetization conditions of the double-junction π rings are deduced. For the multi-junction π rings consisting of more than two junctions, mathematical computation is needed to analyse the Φ–Φx and f–i relations. In the conditions where the absolute critical current value of each junction is equal and there are hystereses on the Φ–Φx characteristic curve, the system has spontaneous magnetization solutions. However, the non-spontaneous magnetization state with zero circulating current is a metastable state with local minimum free energy; therefore, the multi-junction π ring system probably would not spontaneously magnetize.

We attempt to make MgB2 thin films by using a pulsed-laser-deposition (PLD) and a magnetron sputtering method. We have deposited metal magnesium and boron on various substrates under different vacuum conditions. The PLD method has been employed to fabricate layers of magnesium and boron sandwiches under room temperature and the multi-layer system was then annealed in-situ under different temperatures. We also attempted to co-deposit magnesium and boron under high vacuum (5 × 10−5 Pa) on heated substrates with PLD. We have successfully grown superconducting MgB2 thin films on an STO (100) substrate by magnetron sputtering. The onset transition temperature was 37 K and zero resistance temperature was 34 K.

We report on the research work at Peking University on optimizing high-temperature superconductor (HTS) rf superconducting quantum interference device (SQUID) systems and applying them in geophysical survey and magnetocardiography (MCG). Emphasis is placed on the design of comb-shape resonators for HTS rf SQUID systems and the experimental results of two applications: transient electromagnetics and MCG. The magnetic-field sensitivity of HTS magnetometers is now adequate for MCG applications. However, in order to be commercially used, the system still needs some improvements: development of suitable gradiometers and multi-channel systems.

The proximity effect in multilayer structures with dirty two band superconductors and ferromagnets is investigated here. With a homogeneous exchange field and interband scattering in the ferromagnetic layer, the condensate functions that penetrate the ferromagnet are coupled up. This coupling effect is intensively suppressed by the exchange field and modulated by the diffusion coefficients of the two bands. Such coupling also affects the superconductor where the condensate functions of the two bands are also coupled up through the proximity effect. An inhomogeneous exchange field raises the damped oscillation of the condensate functions as the spatial distance from the interface increases. There is a 0−π phase shift when the ferromagnetic layer thickness varies beyond the ferromagnetic coherence length.

The technique of electron beam annealing for fabricating MgB2 thin films has been explored. MgB2 thin films were prepared by e-beam evaporation of M?B precursor films on 6H?SiC (0001) substrates followed by ex?situ electron beam annealing without any extra Mg vapor or argon gas protection. The very short annealing duration, about 1?s, effectively prevented volatilization and oxidation of Mg and decomposition of MgB2. In comparison with the MgB2 thin films grown by other techniques, our films show medium qualities including a superconducting transition temperature of Tconset ~ 35.3?K, a transition width ?Tc ~ 0.2?K, and a critical current density of Jc(5?K, 0?T) ~ 3.2 ? 106?A?cm ? 2. Such an electron beam annealing technique has potential for the fabrication of large-scale MgB2 thin films as well as MgB2 wires and tapes.