Enhanced superconducting properties in epitaxial FeSe thin films with self-assembled Fe3O4 nanoparticles

In this paper we report epitaxial tetragonal iron selenide thin films grown on single crystal SrTiO3 (STO) (0 0 1) and MgO (0 0 1) substrates by a pulsed laser deposition (PLD) technique. Deposition temperature and annealing process are found to be critical for achieving the tetragonal phase and the optimum superconducting properties of the films. The critical transition temperature of the thin films ranges from 2 K to 11.5 K depending on the deposition temperature and annealing condition. The samples with higher critical transition temperatures show better film crystallinity along with self-assembled Fe3O4 nanoparticles (∼15 nm in average particle size) in the films according to both X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. Besides the better crystallinity achieved in the films, the formation of Fe3O4 nanoparticles could assist the formation of the tetragonal FeSe phase and thus lead to the enhanced superconducting properties.

► Epitaxial tetragonal FeSe thin films were deposited by pulsed laser deposition.
► Deposition temperature and annealing process are critical for achieving the optimum superconducting properties of the films.
► The optimum deposition temperatures are ∼500 °C and 550 °C for samples on STO and MgO substrates, respectively.
► The self-assembled Fe3O4 nanoparticles were found to have a direct correlation with the optimum superconducting properties of the films.