Flux Pinning in Y- and Ag-Doped MgB&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;

Jack Dyson,Anna Tampieri,Simone Sprio,Gianni Albertini,Gianni Barucca,Daniele Rinaldi

doi:10.4236/ampc.2015.510043

Abstract

High temperature superconductor research is presently concentrated upon the flux pinning properties of the Abrikosov lattice of the mixed-mode superconducting phase. The temperature thermal fluctuations, current and magnetic field unpin the flux vortices and so cause electromagnetic resistivity in high temperature superconductors. Materials with higher vortex pinning exhibit less resistivity and are more attractive for industrial uses. In the present article, we measured and correlated the pinning flux energy barrier, determined by AC magnetic measurements, and transmission electron microscopy measurements to the critical current Jc in Yttrium- and Silver-doped MgB2 superconductors. The energy of the flux vortex was evaluated as a function of the magnetic field. The energy barrier curves suggest an optimal doping level to occur in doped materials. This result only depends on the optimal size and distribution of precipitates, and not on their chemical composition. The energy barriers have been compared with that of undoped MgB2 in literature.

Highlights

Magnesium diboride MgB2 BCS-type superconductors (SCs) are widely used in sensors, electric power applications and electronic devices
The effectiveness of doping to increase the energy barrier is deduced after comparing these experimental data with those obtained from undoped MgB2 samples reported in literature
Senatore et al compared the experimental results of AC measurements in Bulk MgB2, with susceptibility curves obtained by numerical calculations, assuming a nonlinear diffusion equation for the magnetic field

Summary

Introduction

Magnesium diboride MgB2 BCS-type superconductors (SCs) are widely used in sensors, electric power applications and electronic devices. Scope of this work is to clarify the influence of Silver and Yttrium doping agents (at our best knowledge the latter was rarely studied) on the height of the vortex energy barrier This last is a fundamental property for improving the superconducting critical current in the presence of external magnetic fields. In a previous study of MgB2 [23], it was discussed that the sample purity and density were not directly related to the superconducting properties, while the pinning centres were suggested to play a fundamental role Interesting results in this sense were obtained with small amounts of Ag and Y doping. In order to make this last point clear, our results are compared with those reported in literature in the case of undoped MgB2 samples, either synthesized as bulk or as film

Experimental

Results and Discussion

Conclusions