Thickness dependence of critical current density inMgB2 films fabricated by ex situ annealing of CVD-grown B films in Mg vapor

Abstract

A study was performed to examine theJc behavior as a function ofthickness in MgB2 films fabricatedby ex situ annealing at 840 °C of boron films, grown by chemical vapor deposition, in Mg vapor. The film thicknesses range between 300 nmand 10 µm. Thevalues of Jc range from 1.2 × 107 A cm−2 for 300 nmto 1.9 × 105 A cm−2 for10 µm film thicknesses at 20 K and self-field. The study shows that the critical current density(Jc)in MgB2 films decreases with increasing film thickness, similar to that observed inYBCO-coated conductors. Moreover, our study shows that critical current(Ic) reaches itsmaximum value of 728 A cm−1 width at ∼1 µm thick MgB2 films at 20 K and self-field, which is, interestingly, the same thicknessof pulsed-laser-deposited YBCO-coated conductors at whichIc reaches its maximumvalue. The high Jc values carried by our films show that the ex situ fabrication method can produce high qualityMgB2 films at low processing temperatures, which is promising for RF cavity applications andcoated-conductor wires and tapes.