Magneto-optical visualization of vortices penetration into Ba(Fe1.8Co0.2)As2

Abstract

Vortices penetration into oxygen-free superconducting compounds FeAs-122 system is of interest in understanding superconductivity. This work studies the vortices motion in Ba(Fe1.8Co0.2)As2 single crystal by means of magneto-optical imaging technique in zero field cooled and field cooled conditions. The captured magneto-optical images and corresponding flux profiles show that, at zero field cooled condition, vortices penetrate into the crystal from the edges as external magnetic field increases. A vortices-free region is observed at the center of sample as applied field is less than full penetration field. In field cooled condition, the introduced vortices leave the sample at the edges as field decreases and polarization of the vortices at the edges are opposite as decreasing field approaches to zero. The pinning strength decreases with increasing temperature. The observed vortex behavior is very similar to that in high Tc superconducting materials with strong pinning strength.