Martin Luther University Halle-Wittenberg

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A2: Magnetoelectric coupling in wurtzite-perovskite-spinel heterostructures grown by laser-MBE

Multiferroic composites with different dimensionalities of the building blocks may show remarkably higher magnetoelectric coupling in comparison to single-phase multiferroics due to interface effects. Therefore, such composites are promising for applications. For example, the magnetoelectric voltage coefficient αME of a 2-2 superlattice built from ferroelectric BaTiO3 and multiferroic BiFeO3 is much higher as that of a single-phase epitaxial BiFeO3 film.

In the following, we will investigate the correlation of magnetoelectric coupling and microstructure as well as magnetic spin structure of multiferroic BaTiO3-BiFeO3 composite films. The understanding of strain-mediated coupling on a microscopic length scale will support the enhancement of magnetoelectric coefficients, thus making composites suitable for device applications. Currently, the magnetoelectric coefficient of our epitaxial BaTiO3-BiFeO3 superlattices reaches state-of-the-art values of 24 V/(cmOe) at 300 K. Probably, oxygen vacancy superstructures and antiphase-tilt of the oxygen octahedra in the single layers determine the magnetoelectric coupling of the composite films. Such defects, as well as the microscopic strain state shall be investigated with high-resolution TEM. Due to a targeted selection of the ferrelectric and magnetic / multiferroic components of the composite films and control of defect densities and geometric dimensionalities, magnetoelectrics ready for applications shall be provided finally.

Another research field is electrical conductivity in low-ordered spinell, tetragonal TiO2-, and LaNiO3-LaAlO3 films. Pentcheva et al. (2014) proposed theoretically topological phases in LaNiO3-LaAlO3 (111) superlattices. First experiments with LaAlO3-LaNiO3 superlattices show in dependence on the single-layer thickness in the range from 1.2 nm to 10 nm an up to now not completely understood metal-insulator transition. These investigations shall be extended to other highly-correlated oxides such as LaAuO3, LaAgO3, and SrIrO3.

Principal Investigator

Prof. Dr. Michael Lorenz ⇒

phone: +49 (0) 341/97 32661

fax: +49 (0) 341/97 39286

Prof. Dr. Michael Lorenz

Prof. Dr. Michael Lorenz