Anisotropies in the critical currents of NbN films

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Abstract
Anisotropies in the critical currents have been measured for NbN films prepared by reactive sputtering. The Ic values are anisotropic with respect to the orientation of the external field in the plane perpendicular to the direction of the current flow in the film. The effects of the substrate, field strength, and heat treatment on the Ic-θ characteristics were examined. The Ic values show an enhanced peak at θ = 90°, where the external field is applied perpendicular to the film surface. The peak at θ = 90° is explained in terms of the film structure of NbN films, which show a columnar polycrystalline growth.