Hexagonal ferrites were discovered more than 60 years ago but only quite recently two effects were found - magnetoelectric (ME) effect and spin Seebeck effect. There is a need for preparation of epitaxial or strongly oriented thin films. This is possible even in the case the thin film and substrate have different structures or large mismatch in the lattice parameters. Then the strong orientation can be achieved if a polycrystalline film is deposited first and then heated to break up into isolated grains (seeds). This is followed by deposition of thicker layer when the isolated islands can act as nucleation centers for the growth of a highly oriented film.
In this work, thin films of Ba2Zn2Fe12O22 (Y) ferrite were prepared through the chemical solution deposition method using SrTiO3(111) (STO) substrates and the above two-step process. As seeding layers two types of materials were used - oriented films with hexagonal symmetry in layer of O2-: cubic 111-oriented cobaltates, namely CoFe2O4 and hexagonal 00l-oriented M-ferrites. The former were prepared through the transformation of 00l-oriented layered cobaltates Na(CoFe)O2 [1] and for the choice of the latter a set of M-ferrites with different lattice mismatch with respect to the STO substrate and also to the Y-ferrite top films, different chemical composition and different magnetic properties were tested. The best orientation of this Y-ferrite film achieved for hexagonal M-seed layer with composition (BaSr)(GaAl)12O19, Ba(FeAl)12O19 [2].
The samples were studied by X-ray diffraction (XRD), electron back-scatter diffraction (EBSD) and atomic force microscopy. XRD analysis was performed in both conventional Bragg-Brentano symmetric setup as well as in parallel beam with the Eulerian cradle. In order to find appropriate reference value of lattice parameters of different used seed layers, some data analysis of PDF-4 database had to be performed with respect to the statistics and/or also to the stoichiometry. Structural studies were focused to investigation of preferred orientation by symmetric and asymmetric XRD scans and by EBSD and also to the analysis of possible residual stresses.
This work was supported by the Grant Agency of the Czech Republic under Grant No. 14-18392S.