Deposition of perpendicular c-axis oriented BaM thin films on (001) Al2O3 substrates by introducing an interfacial BaM buffer layer

• BaM thin films were deposited on (001) Al2O3 substrates by RF magnetron sputtering.
• Single layered and double layered BaM films deposited at different Ts were studied.
• The single layered films are both randomly c-axis oriented.
• The double layered film is perpendicularly c-axis oriented with an epitaxial texture.
• The mechanism is attributed to the change of nucleation sites and release of stress.

M-type barium ferrite (BaM) thin films with two different structures (single layered and double layered) were deposited on (001) Al2O3 single crystal substrates using an RF magnetron sputtering system. The changes in the surface morphologies, crystallographic and magnetic properties of BaM thin films corresponding to the different structures and substrate temperatures (Ts) were investigated in detail. The results indicated that the interfacial BaM buffer layer plays an important role in improving the crystallographic and magnetic properties of BaM thin films. The single layered BaM thin films deposited at Ts=300 °C and Ts=500 °C are both randomly c-axis oriented. Whereas, by introducing a thin BaM layer which acts as an interfacial buffer layer, an excellent perpendicular c-axis orientation with an epitaxial structure for the double layered BaM thin film was obtained. The c-axis dispersion angle (Δθc) decreased to 0.49°, and the perpendicular squareness ratio increased to 0.85 for the double layered film. The mechanism for improving the perpendicular c-axis orientation with an interfacial BaM buffer layer was attributed to two reasons. One is a relative increase in the nucleation sites for perpendicularly oriented grains over the nucleation sites for in-plane and/or randomly oriented grains, and the other is the release of the stress that comes from the interface between BaM thin film and Al2O3 substrate.