Influence of ion implantation on the magnetic and transport properties of manganite films
Résumé
We have used oxygen ions irradiation to generate controlled structural disorder in thin manganite films. Conductive atomic force microscopy (CAFM) and transport and magnetic measurements were performed to analyze the influence of the implantation process in the physical properties of the films. CAFM images show regions with different conductivity values, probably due to the random distribution of point defect. The transport and magnetic properties of these systems are interpreted in this context. Metal-insulator transition can be described in the frame of a percolative model. Disorder increases the distance between conducting regions, lowering the observed T-MI. Point-defect disorder increases localization of the carriers due to increased disorder and locally enhanced strain field. Remarkably, even with the inhomogeneous nature of the samples, no sign of low-field magnetoresistance was found. Point-defect disorder decreases the system magnetization but does not seem to change the magnetic transition temperature. The coercive field of the samples increases linearly with increasing disorder but decreases when disorder is higher than a critical value.