Structural study of thin-film PbTiO$_3$-CoFe$_2$O$_4$ composition spreads

Multiferroic materials exhibiting magnetoelectric (ME) effects are of great interest for novel devices. In multiphase systems, the ME effect arises from the elastic interaction of ferromagnetic and ferroelectric phases. Recently we studied properties and structures of multiferroic PbTiO$_{3}$ (PTO) and CoFe$_{2}$O$_{4}$ (CFO) thin films produced by a composition-spread technique. The compositional spread was achieved by PLD of a superlattice of pure PTO and CFO. Here we report results of cross-sectional TEM studies, which can be summarized as following: a. For all compositions the microstuctures yielded pseudo-binary two phases equilibrium of PTO and CFO, and the phases are epitaxial to each other and to a MgO substrate; b. Morphology of the phases strongly depends on a thickness of the deposited superlattice; c.The most pronounced ME effect was found for a pancake-like morphology; d.Diffusional re-arrangement of layers during the deposition results in the solubility of CFO in PTO, which drastically reduces ferroelectric Curie temperature of PTO.