Raman spectroscopic investigations of epitaxial multiferroic thin films

在多铁性、铁电性和铁磁材料中，决定基本铁性性质的晶格动力学可以通过应变工程以受控的方式受到影响。本计画将利用拉曼光谱系统地研究应变对外延薄膜（如BiFeO_3和CoFe_2 O_4）中光学声子的影响。为此，应变将由压电衬底（例如PMN-PT）引起。该方法允许区分由应变引起的效应与重叠的非本征效应（由生长条件或不同的衬底质量引起），所述重叠的非本征效应通常在通过在具有不同晶格参数的衬底上生长期望的膜来执行应变工程时发生。该项目的另一个重点在于铁电/磁性异质结构的拉曼光谱研究。铁电/磁性复合系统（例如BiFeO 3/CoFe 2 O 4）由于组成材料的大极化和磁化而在室温下具有多铁性。我们将利用磁场相关的拉曼光谱来研究这种系统中的磁弹性耦合。具体来说，我们将比较磁致伸缩的影响，拉曼活性声子的BiFeO 3/CoFe 2 O 4双层和自组装（柱/矩阵）BiFeO 3/CoFe 2 O 4系统，以评估磁致伸缩耦合的纳米结构的大小的影响。

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.