High intergranular critical currents in metallic MgB₂superconductor

Abstract

Strong evidence for high intergranular critical current densities and large bulk magnetic flux pinning in superconducting polycrystalline MgB 2 has been observed. The presence of strongly-coupled grain boundaries in this material has been confirmed by a dramatic collapse of the magnetic hysteresis loop when a bulk specimen is ground into a fine powder and re-measured under similar conditions. Further evidence for strong intergrain links in polycrystalline MgB 2 is provided by the continuous variation of the remanent magnetic moment up to the full penetration field of a bulk sample. The absence of weak-link nature in this material has profound implications for its potential in a wide range of engineering applications.

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

“…High transport critical current densities have been reported in MgB 2 bulk samples [2]- [4]. Due to its intermediate transition temperature, weak-link free grain boundaries [5] and low material cost, this material is interesting for potential applications such as MRI (magnetic resonance imaging) and transformers at operating temperature of 20-30K.…”

Anisotropic superconducting properties ofMgB2single crystals probed by in-plane electrical transport measurements

“…Transport and magnetization measurements of the upper critical field [4][5][6][7][8] and critical current density 9,10 of MgB 2 revealed properties typical for a type-II superconductor. Since crystal structure of MgB 2 consists of alternating Mg and B sheets, electronic anisotropy of this material may be expected.…”

Current Percolation and Anisotropy in PolycrystallineMgB2

“…25.Sv Soon after the discovery of superconductivity in MgB 2 [1], it was found that grain boundaries do not limit the current flow in polycrystalline samples [2,3]. Thus, sintered bulk samples and wires could be prepared with critical current densities appropriate for technical applications at low magnetic fields [4].…”

“…The resistive transition of a sintered bulk sample [3] was measured at fixed magnetic field at a current density of 2 kA/m 2 . The onset of the transition was defined at 95 % of the normal state resistance, the offset at 5 %.…”

“…In order to evaluate this expression numerically, 1001 grains were chosen with sin(θ) equally distributed between 0 and 1. Their critical currents were calculated according to (3) and the probability distribution p was calculated basically by counting the number of grains with a critical current density above a certain value. The integral was then replaced by a summation over the discrete critical current densities of the chosen grains.…”