## 3 Results and Discussion
### Substrate Stage Rotation Rate Effects  
In order to investigate the somewhat unexpected effect of substrate stage rotation rate on the MO properties of this type of garnet materials, we deposited three batches of films (named S\({}_{\text{S1}}\), S\({}_{\text{S2}}\), and S\({}_{\text{S3}}\)) onto quartz substrates using three different substrate stage rotation rates (7.5-8, 15.5-16, 25.5-26 revolutions per minute (rpm)). Substrate stage rotation is widely used in most (or all) physical vapor deposition technologies and is known to improve the area uniformity of the deposited film thickness. Relatively few studies reported so far in the literature have concentrated on uncovering other effects of substrate rotation rate on the functional properties of thin films, e.g., [21; 22]. Initially, we did not expect the MO quality factor in magnetic garnets to be significantly dependent on the substrate stage rotation rate; however, it was found that an optimum rotation rate existed, at least for this composition type. For each batch of samples, all other deposition process parameters were kept identical. All three batches of samples were annealed in one annealing run using the best-identified annealing regime for garnet films of this stoichiometry type (6 h at 580 \({}^{\circ}\)C or, alternatively, 1 h at 670 \({}^{\circ}\)C), which was found by running multiple annealing experiments. The optical absorption coefficients were software-fitted using spectrophotometry measurement results across the entire visible spectral range (Figure 3a). There were significant (and initially completely unexpected) differences observed in the MO properties of films fabricated at different substrate stage rotation rates (in terms of the MO figure of merit); a summary of measured properties is shown in Table 2.  
The samples prepared using the 15.5-16 rpm substrate stage rotation rate repeatedly showed a better MO performance (in terms of the specific Faraday rotation and the MO figure of merit measured at 532 nm). These samples also had lower coercive force and saturation magnetization values compared with the films prepared using higher substrate stage rotation rates, as shown in Table 2. We repeated the deposition and annealing processes more than once, and again observed the same trends in the dependency of the MO properties on this process parameter. Figure 3: _Cont._Figure 3: _Cont._  
Figure 3b shows the data on the substrate stage rotation-frequency-dependent evolution of the measured MO figure of merit obtained in Bi\({}_{2.1}\)Dy\({}_{0.9}\)Fe\({}_{3}\),\({}_{9}\)Ga\({}_{1.1}\)O\({}_{12}\) films prepared on quartz substrates. The data point distributions within the data clusters shown within the circles followed the observed trend of the MO quality factor for each of the annealing regimes used. Both of the annealing regimes (6 h at 580 \({}^{\circ}\)C and 1 h at 670 \({}^{\circ}\)C) had been previously established for this material type based on a large number of trials; each processing regime led to the best achievable results in terms of the optical and MO quality of films. The prominent peaks observed in the XRD patterns of samples S\({}_{\text{S1}}\), S\({}_{\text{S2}}\), and S\({}_{\text{S3}}\) indicated that the garnet layers were grown homogeneously on the quartz substrates, even though there were some small differences in the peaks' angular positions (Figure 3c). These differences may  
Figure 3: Fitted optical absorption coefficients spectra across the visible spectral region and the MO figure of merit data points measured at the 532 nm wavelength for the annealed garnet layers (**a**,**b**); X-ray diffraction datasets obtained for films deposited at different substrate rotation rates (**c**); the measured concentrations (atomic %) of the five elements found to be present in the sputtered garnet (as-deposited) layers (**d**).