Low temperature X-ray imaging of magnetic flux patterns in high temperature superconductors

Claudia Stahl,Markus Weigand,Gisela Schütz,Stephen Ruoß,Joachim Albrecht,Michael Bechtel

doi:10.1063/1.4907764

Abstract

We present X-ray magnetic circular dichroism (XMCD) microscopy results obtained at liquid nitrogen temperatures on the high-Tc superconductor YBCO (YBa2Cu3O7–δ). The magnetic flux distribution arising from electric currents in the superconductor is detected and visualized using soft-magnetic Co40Fe40B20 (CoFeB) as sensor layer and XMCD as contrast mechanism. It has been shown that the XMCD contrast in the sensor layer directly corresponds to magnetic flux distribution of the superconductor and hence can be used to image magnetic structures in superconductors [Stahl et al., Phys. Rev. B 90, 104515 (2014)]. The existing scanning UHV X-ray microscopy setup MAXYMUS at the synchrotron BESSY II in Berlin has been upgraded for that purpose: we use a nitrogen based MMR Micro Miniature Joule-Thompson Cryostat with temperature range from 75 K to 580 K. The capability of the method is demonstrated on two different superconducting samples, an optimally doped thin film and a melt-textured block.

Highlights

For applications of high-Tc superconductors as well as for the fundamental understanding of the electrical transport, the knowledge of pinning and motion of flux lines is a prerequisite.[2,3] In an external magnetic field pinning leads to the evolution of gradients of the magnetic flux density
We present X-ray magnetic circular dichroism (XMCD) microscopy results obtained at liquid nitrogen temperatures on the high-Tc superconductor YBCO (YBa2Cu3O7–d)
The magnetic flux distribution arising from electric currents in the superconductor is detected and visualized using soft-magnetic Co40Fe40B20 (CoFeB) as sensor layer and XMCD as contrast mechanism

Summary

INTRODUCTION

For applications of high-Tc superconductors as well as for the fundamental understanding of the electrical transport, the knowledge of pinning and motion of flux lines is a prerequisite.[2,3] In an external magnetic field pinning leads to the evolution of gradients of the magnetic flux density. For magneto-optical imaging based on the Faraday Effect, iron garnet films are widely used.[5] These sensor layers are sensitive to the out-of-plane component of the magnetic flux density. It opens up the possibility of investigating high-Tc superconductors at liquid nitrogen temperatures. We demonstrate the possibilities of imaging the magnetic flux distribution in superconductors on two different kinds of samples, namely, a YBCO thin film and a melt-textured YBCO. Both superconductors are covered with the sensor layer, namely, CoFeB

BILAYER CHARACTERISTICS AND LOW TEMPERATURE SETUP

IMAGES OF THE MAGNETIC FLUX DENSITY

CONCLUSION