Use of magnetoplumbite and spinel ferrite seed layers for the growth of oriented Y ferrite thin films

Thin films of Ba2Zn2Fe12O22(Y) ferrite were prepared on SrTiO3(111) single crystal substrates using chemical solution deposition method and two-step crystallization process. A polycrystalline film of seeding phase was deposited first and then heated to break it up into isolated grains that acted as nucleation seeds for crystallization of Y phase. These seed grains modify the high lattice and chemical mismatch of the SrTiO3(111)/Y hetero-interface by creating two interfaces with reduced mismatch. Two epitaxially grown structures with hexagonal symmetry of the O2- ion layers were used for seeding, namely the cubic (111)-oriented CoFe2O4 and the hexagonal (001)-oriented (BaSr)(GaAl)12O19. Atomic force microscopy and X-ray diffraction measurements show that the Y films grow with the c-axis perpendicular to the surface, matching the orientation of the seed layer. The Y film with the best orientation was obtained for (BaSr)(GaAl)12O19 seed layer despite its large misfit with respect to the Y phase. The mechanisms leading to the experimentally observed structures and morphologies are discussed with respect to the influence of lattice mismatch between the relevant structures, and surface coverage and surface topography of the seed layers.