Tunnel transport through CoFe2O4 barriers investigated by conducting atomic force microscopy

Conducting atomic force microscopy has been used to monitor the quality of spin-filtering CoFe2O4 tunnel barriers by mapping current as a function of their thickness. We show that appropriate film annealing leads to a substantial improvement of their tunnelling properties. The contact force between tip and sample was identified to have a determining influence on the width of the distribution P(I) in current maps, thus precluding its reliable use to infer barrier characteristics. Therefore, assessment of tunnel transport should be done by means of the typical current which is a well-defined parameter at a given contact force, rather than by the current distribution width.