Thin films and superlattices of multiferroic hexagonal rare earth manganites

Hexagonal YMnO3 and HoMnO3 as well as (YMnO3/HoMnO3)15 superlattices were grown on (111) ZrO2 (Y2O3) and (111) Pt/TiO2/SiO2/p-type (100)Si substrates. Epitaxial stabilization was used on the same substrates to grow DyMnO3 or TbMnO3 (which normally crystallize in an orthorhombic, perovskite-type, structure). All heterostructures were obtained oriented, with the c-axis of the hexagonal cell perpendicular to the substrate plane. This orientation is desired since it is the direction of the ferroelectric polarization in hexagonal manganites. The strain state of the films grown on conductive Pt electrodes, tracked by the evolution of the c parameter as a function of film thickness, was found to be completely different than the one obtained on YSZ. Such a study is important for future strain engineering in multilayers. High-resolution transmission electron microscopy on superlattices grown on (111)Pt indicates a high crystalline quality along the c-axis and sharp interfaces.