Enhanced flux pinning properties in superconducting FeSe _0.5Te _0.5 thin films with secondary phases

In this paper we report epitaxial superconducting FeSe _0.5Te _0.5 thin films grown on single crystal SrTiO ₃ (STO) (100) substrates by a pulse laser deposition (PLD) technique. The films include a single layer grown under vacuum, a single layer grown in controlled oxygen atmosphere and a tri-layer film with a 7nm thick CeO ₂ interlayer. All the films show a similar transition temperature T _c ranging from ∼ 12K (T _c ^onset) to ∼ 10K (T _c ^zero), while the CeO ₂ nanolayer sample shows a significantly enhanced critical current density under magnetic field. The calculated critical current density of the film with the CeO ₂ interlayer is ∼ 10 ⁵Acm ² at 2K in self-field and 2.8×10 ⁴Acm ² at 7T at 2K. The power-law exponent value of the sample is determined to be as low as 0.21 at 2K. Microstructural analysis shows that both the oxygen grown sample and the sample with the CeO ₂ nanolayer have uniform nanoclusters in the film matrix. These secondary phases as well as the defects around the interlayer interfaces might be responsible for the enhanced pinning properties.