Anisotropic critical currents inFeSe0.5Te0.5 films and the influence of neutron irradiation

Abstract

We report on measurements of the superconducting properties ofFeSe0.5Te0.5 thin films grown on lanthanum aluminate. The films have high transition temperatures(above 19 K) and sharp resistive transitions in fields up to 15 T. The temperaturedependence of the upper critical field and the irreversibility lines are steep and anisotropic,as recently reported for single crystals. The critical current densities, assessedby magnetization measurements in a vector VSM, were found to be well above109 A m − 2 at low temperatures. In all samples, the critical current as a function of field orientation has amaximum, when the field is oriented parallel to the film surface. The maximum indicates thepresence of correlated pinning centers. A minimum occurs in three films, when the field isapplied perpendicular to the film plane. In the fourth film, instead, a local maximum caused byc-axis-correlated pinning centers was found at this orientation. The irradiation oftwo films with fast neutrons did not change the properties drastically, wherea maximum enhancement of the critical current by a factor of two was found.