Raman spectroscopic investigations of epitaxial multiferroic thin films

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In multiferroic, ferroelectric, and ferromagnetic materials the lattice dynamics, which determine the fundamental ferroic properties, can be influenced in a controlled way by strain engineering. In this project a systematic study of the strain influence on the optical phonons in epitaxial films (such as BiFeO3 and CoFe2O4) will be performed by Raman spectroscopy. To this purpose, the strain will be induced by a piezoelectric substrate (such as PMN-PT). This method allows to distinguish the effect induced by strain from overlapping extrinsic effects (caused by growth conditions or different substrate quality) that usually occur when the strain engineering is performed by growing the desired films on substrates with different lattice parameters. Another focus of this project lies in the Raman spectroscopic investigation of ferroelectric/magnetic heterostructures. Ferroelectric / magnetic composite systems (as for example BiFeO3 / CoFe2O4) have multiferroic properties at room temperature, due to the large polarization and magnetization of the component materials. We will investigate the magnetoelastic coupling in such system by employing magnetic-field-dependent Raman spectroscopy. Specifically, we will compare the magnetostriction influence on the Raman-active phonons for BiFeO3 / CoFe2O4 bi-layers and self-assembled (pillar/matrix) BiFeO3 / CoFe2O4 systems to assess the effect of the size of the nanostructures on the magnetoelastic coupling.