Low anisotropic upper critical fields in SmO_1−xF_xFeAs thin films with a layered hybrid structure

We report on the upper critical fields in SmO_1−xF_xFeAs thin films prepared by pulsed laser deposition. With an F-content gradient along their thickness, the films could be described approximately as layered two-phase hybrid structures comprised of one superconducting layer and one antiferromagnetic layer. An analytical characterization of different thin film samples by Auger electron spectroscopy and energy-dispersive x-ray spectroscopy in scanning transmission electron microscopy is provided and structural defects, such as antiphase boundaries, were confirmed for films grown at lower deposition temperatures. Electrical transport measurements in pulsed magnetic fields yielded upper critical fields higher than 80 T with an anisotropy γH_c2 ≤ 2.25.