MTL Annual Research Report 2011

We are studying BiFeO₃/CoFe₂O₄ oxide composite thin films, which have the remarkable characteristic of self-assembling into vertical nanostructures during their deposition on a single crystal substrate, typically SrTiO₃. Through the characterization of the structural (Figure 1), magnetic, and electric properties of samples deposited under varying conditions, we are studying the processes happening during deposition that govern the self-assembly of such thin films. A better understanding of the magnetoelectric coupling and strain relationships, due to the coherent interfaces between the three phases, will allow us to fine-tune their magnetic, ferroelectric and multiferroic properties for potential applications.

We demonstrated that these hetero-structured thin films can successfully be grown using a novel alternated-target deposition method, where two ceramic targets of single component BiFeO₃ and CoFe₂O₄ are successively moved under the laser beam for ablation for a given number of pulses (Figure 2). The ratio of pulses on the two targets allows good control of the composition of the film, whereas the total number of cycles controls the thickness of the film. In contrast to the commonly used deposition by ablation from a single target, this alternated method allows fine-tuning of the average composition of the film at different stages of the growth, without the need to fabricate a new target for each desired ratio of the two phases.