The effect of nanoscale Fe doping on the superconducting properties ofMgB2

Abstract

Iron is an important sheath material for fabrication ofMgB2 wires. However, the effect of Fe doping on the superconducting properties ofMgB2 remains controversial. In this work, we present results on nanoscale Fe particle doping inMgB2. The Fe doping experiments were performed using both bulk and thin film forms. Neitherfree Fe particles nor FeB compound was detected at 1% Fe doping by means of eithertransmission electron microscopy (TEM) or x-ray diffraction (XRD), suggesting that Fesubstituted for Mg in the lattice. The level of Fe substitution for Mg is estimated to occurat a level lower than 1% of Mg, and this substitution is proposed to be responsible for thedecrease in transition temperature with Fe doping. Because of the high reactivity of nanoscaleFe particles, Fe doping is largely in the form of FeB at a Fe doping level of 2% whileFe2B was detected at 10% Fe doping by means of both XRD and TEM. TheJc(H) performance was severely depressed at above a 2% doping level. The detrimental effect of nanoscale Fedoping on Jc(H) is attributable to both the Fe substitution for B in the lattice structure and the inclusionsof Fe and FeB which act as weak links at grain boundaries.