Effects of BaM Interfacial Layer on the $c$ -Axis Orientation of BaM Thin Films Deposited on SiO $_{2}$ /Si Substrates

M-type barium ferrite (BaM) thin films with two different structures (single layered and double layered) were deposited on thermally oxidized silicon (SiO 2 /Si) substrates by radio frequency (RF) magnetron sputtering. The changes in surface morphologies, crystallographic and magnetic properties of the films corresponding to different structures and substrate temperatures (T s ) were investigated in detail. In the single layered films deposited directly on SiO 2 /Si substrates at T s = 300°C and T s = 500°C respectively, most of the grains are acicular type. XRD data and magnetic properties measurement confirmed that they are both weakly c-axis perpendicularly oriented. However, in the double layered film with first interfacial layer deposited at T s = 300°C and second layer deposited at T s = 500°C, good crystallographic characteristics and excellent perpendicular c-axis orientation were obtained. The c-axis dispersion angle (Δθ c ) decreased to 0.51°C; the lattice parameters were comparable to those of the bulk BaM; the squareness ratio and coercivity of the out-of-plane increased to 0.85 and 338 kA/m, respectively, for the double layered film. The mechanism for improving perpendicular -axis orientation with an interfacial BaM 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 stress that comes from the interface between BaM thin film and SiO 2 /Si substrate.