Thin Film Magnesium Boride Superconductor with Very High Critical Current Density and Enhanced Irreversibility Field

This is the first review on superconducting MgB2 thin films as far as we know.

Over the past 14 years MgB2 has gone from a startling discovery to a promising, applied superconductor. In this article we present a brief overview of the synthesis and the basic superconducting properties of this remarkable compound. In particular, the effects of pressure, substitutions and neutron irradiation on superconducting properties are discussed.

Thin films of MgB2 superconductor were prepared by three different procedures on sapphire and silicon substrates. Boron thin films, ex-situ annealed in magnesium vapour, resulted in textured polycrystalline films with crystal dimensions below about 1000 nm, onset critical temperature Tcon near 39 K and width of phase transition about 1 K. Both, ex-situ and in-situ annealed co-deposited boron and magnesium thin films on sapphire and silicon substrates give smooth nanocrystalli...

Progress in superconducting device and detector technologies over the past decade have realized practical applications in quantum computers, detectors for far-infrared telescopes, and optical communications. Superconducting thin film materials, however, have remained largely unchanged, with aluminum still being the material of choice for superconducting qubits, and niobium compounds for high frequency/high kinetic inductance devices. Magnesium diboride ($\mathrm{MgB}_2$), kno...

The MgB$_2$ superconductor, discovered in 2001, has provided unique compound features of magnesium diboride with much higher critical temperature and critical field compared to NbTi superconductor. Its applications have been expanding owing to its superior energy balance in high-temperature operation and to its excellent stability and operational margin because of the higher critical temperature and heat capacity. This paper reviews the recent advances in MgB$_2$ applications...

The upper critical field Hc2(T) of sintered pellets of the recently discovered MgB_2 superconductor was investigated in magnetic fields up to 16 T. The upper critical field of the major fraction of the investigated sample was determined from ac susceptibility and resistance data and was found to increase up to Hc2(0) = 13 T at T = 0 corresponding to a coherence length of 5.0 nm. A small fraction of the sample exhibits higher upper critical fields which were measured both resi...

With the relatively high critical temperature (Tc) of 39 K1 and the high critical current density (Jc) of > 100000 A/cm2 in moderate fields, magnesium diboride (MgB2) superconductors could offer the promise of important large-scale and electronic device applications to be operated at 20 K. A significant enhancement in the electromagnetic properties of MgB2 has been achieved through doping with various form of carbon (C). However, doping effect has been limited by the agglomer...

The transport of electrical current through a superconductor falls into three broad regimes: non-dissipative, dissipative but superconducting, and normal or non-superconducting. These regimes are demarkated by two definitions of critical current: one is the threshold current above which the superconductor enters a dissipative (resistive) state; the other is the thermodynamic threshold above which the superconductivity itself is destroyed and the superconducting order paramete...

Magnesium diboride superconducting wires give the largest critical current density (Jc) when produced with iron sheath. Because iron is ferromagnetic, it is expected to improve the field dependence of Jc by shielding of the external field for low magnetic fields. However, transport and magnetic measurements of Jc reveal that Jc in MgB2/Fe is improved far beyond the effect of simple magnetic shielding. The transport measurements in external field show that Jc initially decreas...

Oxygen was systematically incorporated in MBE grown MgB2 films using in-situ post-growth anneals in an oxygen environment. Connectivity analysis in combination with measurements of the critical temperature and resistivity indicate that oxygen is distributed both within and between the grains. High values of critical current densities in field (~4x10^5 A/cm^2 at 8 T and 4.2 K), extrabolated critical fields (>45 T) and slopes of critical field versus temperature (1.4 T/K) are o...