Pinning enhancement in MgB2 superconducting thin films by magnetic nanoparticles of Fe2O3

摘要

MgB2 thin films were fabricated on r-plane Al2O3 (({1} overline{{1}} {0} {2})) substrates. First, deposition of boron was performed by rf magnetron sputtering on Al2O3 substrates and followed by a post-deposition annealing at 850 °C in magnesium vapour. In order to investigate the effect of Fe2O3 nanoparticles on the structural and magnetic properties of films, MgB2 films were coated with different concentrations of Fe2O3 nanoparticles by spin coating process. The magnetic field dependence of the critical current density J c was calculated from the M–H loops and magnetic field dependence of the pinning force density, f p(b), was investigated for the films containing different concentrations of Fe2O3 nanoparticles. The critical current densities, J c, in 3T magnetic field at 5 K were found to be around 2·7 × 104 A/cm2, 4·3 × 104 A/cm2, 1·3 × 105 A/cm2 and 5·2 × 104 A/cm2 for films with concentrations of 0, 25, 50 and 100% Fe2O3, respectively. It was found that the films coated with Fe2O3 nanoparticles have significantly enhanced the critical current density. It can be noted that especially the films coated by Fe2O3 became stronger in the magnetic field and at higher temperatures. It was believed that coated films indicated the presence of artificial pinning centres created by Fe2O3 nanoparticles. The results of AFM indicate that surface roughness of the films significantly decreased with increase in concentration of coating material.