Epitaxial growth and properties of Bi-substituted yttrium-iron-garnet films grown on (111) gadolinium-gallium-garnet substrates by using rf magnetron sputtering

Epitaxial films of Bi-substituted yttrium iron garnet (BixY3-xFe5O12, BiYIG) have been grown on (111) gadolinium-gallium-garnet substrates, Gd3Ga5O12, by using rf magnetron sputtering. As the film thickness is increased, the film structure varies from a single layer to a double layer due to the stress that develops in the films. A film with a thickness below some critical value has a single layer, which is in a compressive stress state due to the lattice-constant mismatch between the film and the substrate. A film with a thickness above some critical value has a double layer: lower and upper layers. The former is in a compressive stress state like a single-layer film; the latter is unstrained due to the stress relief provided by the formation of misfit dislocations. All the BiYIG films studied here exhibit granular-like surface features with grain sizes of about 50 similar to 200 nm and have surface roughnesses of 0.65 similar to 2.5 urn. The BiYIG films also have in-plane magnetic anisotropy, which is advantageous in the fabrication of planar waveguides.