Substrate effects on the crystalline orientation of barium hexaferrite films

Abstract

In situ crystallized barium hexaferrite films have been deposited with a target-facing sputtering system under previously optimized conditions on four different substrates which are: SiO2, ZnO, Gd3Ga 5O12, and Al2O3. By using several structural and magnetic characterizations different growth mechanisms were put forward according to the chosen substrate. On amorphous silica there is an important Ba affinity for SiO2, resulting in the formation of a glass layer with high Ba and Si concentrations. Then comes a (111) spinel which is magnetite and above it there is the well c-oriented Ba hexaferrite (Δω=2.3°). Under progressive annealings, magnetite changes into maghemite and then into hexaferrite. On (001) ZnO, another (111) spinel is formed, that is ZnFe2O4 on which textured Ba hexaferrite film is grown (Δω=1.3°). Under high-temperature annealings ZnO decomposes little by little, on the one hand into ZnFe2O4 and on the other hand, through a diffusion process across the Ba hexaferrite into a surface layer rich in Ba and Zn. On GGG and Al2O3 there are no intermediate layers. In the former case a well c-axis-oriented Ba hexaferrite (Δω=3.6°) was observed whereas for the latter case the orientation of the hexaferrite was found to be random.