Magnetic flux distribution in YBCO thin films investigated via XMCD microscopy at low temperatures

The magnetic flux distribution of high-T_c YBa₂Cu₃O_7-δ (YBCO) thin films exhibits structures within the submicrometer regime. Therefore scanning x-ray microscopy based on the x-ray magnetic circular dichroism effect (XMCD) is our method of choice revealing very high spatial resolution of both surface structure and magnetization distribution. Introducing an XMCD sensitive, soft-magnetic CoFeB respectively Py sensor layer wherein the magnetic stray field of the superconductor is mapped, the critical current density and its dependency of the defect structure in the YBCO thin films are imaged and analyzed. The measurements were carried out at the scanning x-ray microscope MAXYMUS at Bessy II, HZB Berlin utilizing a new low temperature setup.