Controlling Bi/Fe ratio in bismuth iron garnet thin films deposited by confocal magnetron sputtering for enhanced Faraday rotation

We have successfully deposited high-quality bismuth-iron-garnet (BIG; Bi ₃Fe ₅O ₁₂) epitaxial thin films on single crystal gadolinium-gallium-garnet (GGG; Gd ₃Ga ₅O ₁₂) (111) substrates through Radio frequency (RF) confocal sputtering, utilizing separate bismuth and iron oxide sputtering targets and optimized thermal treatments. The Bi/Fe ratio in the deposited BIG thin films can be varied by controlling the sputter process parameters. These deposited thin films exhibit homogeneity and surface root mean square (rms) roughness of less than 2 nm. The epitaxial film quality is confirmed by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). Moreover, the films demonstrate low optical loss and a magneto-optical Faraday rotation as high as − 3 4 o ± 1 o / μ m at a wavelength of 535 nm for a BIG thin film with a Bi/Fe ratio 0.7 and annealing temperature of 51 0 o C . Additionally, the coercivity of the deposited films is lower than that of those deposited via RF sputtering using a single composite target. This co-sputtering approach provides real-time flexibility for the deposition of high-quality BIG films.