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(Fe 1.8 Co 0.2 )As 2 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 pinned vortices leave the sample from the edges as field decreases and polarization of the vortices at the edges are opposite as decreasing field approaches to zero. The pinning strength is decreases with increasing temperature. The observed vortex behaviour is very similar to that in high T c superconducting materials with strong pinning strength.

Instability of vortex-antivortex interface in optimally doped Ba(Fe1−xCox)2<

“…In this paper, we explore the flux penetration in single crystals of Ba(Fe 1x Co x ) 2 As 2 , especially focusing on the influence of a remagnetized field on the nature of the flux front, using MO imaging. Hence our objective goes beyond the known features of the flux patterns in the mixed state previously obtained by MO imaging 18,19,20 . Our observations provide compelling evidence for the presence of turbulent flux instability in a superconductor other than the 123-type cuprates.…”