## 1 Introduction  
Bismuth (Bi)-substituted magneto-optical (MO) garnet materials are very attractive for use in various technological applications such as magnetic memory, magnetoplasmonic devices, magneto-optic sensors, lightwave polarization controllers, and MO spatial or temporal light modulators [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11]. They possess record-high Faraday or Kerr effects simultaneously with low optical losses in parts of the visible and near-infrared regions and are starting to become highly sought after for the development of cost-effective and reliable photonic devices and sensors. Since the 1960s, Bi-substituted MO garnet thin films have been fabricated with different compositional stoichiometries using deposition technologies such as Pulsed Laser Deposition (PLD), Liquid-Phase Epitaxy (LPE), Ion Beam Sputtering (IBS), Reactive Ion Beam Sputtering (RIBS), metal-organic chemical vapor deposition (MOCVD), sol-gel technique, and radio frequency (RF) magnetron sputtering, and using other material synthesis systems [5; 12; 13; 14; 15; 16; 17; 18; 19]. All of these physical vapor deposition techniques require complex and multiparameter process optimizations at both the deposition and annealing (crystallization) stages. RF magnetron sputtering deposition followed by a high-temperature oven crystallization process is one of the most flexible and compatible approaches to synthesizing MO garnet materials. However, there are multiple important process-related factors associated with the preparation of MO garnet thin films that affect their properties and quality. Many of these factors are related to the parameters of the magnetron sputter deposition technique used to fabricate garnet films, such as the substrate type, the substrate temperature, the substrate stage rotation rate, and the deposition environment (process gas(es) and their partial pressure(s)), and need to be controlled carefully to optimize the film properties. Other factors defining the properties of garnet film layers are associated with the annealing process. In the past, several studies have been conducted to investigate the effects of process parameters on the optical and magneto-optical properties of garnet films [20; 21; 22]. It has been reported that the variations of deposition process parameters such as the substrate stage temperature, target rotation frequencies, argon pressure, and RF power densities applied to the sputtering target all affect the properties of garnet thin films through inducing changes in the film morphology and density [21; 22; 23; 24; 25; 26; 27]. Also, the annealing heat treatment regime can affect the optical and MO properties through the crystallization process kinetics by changing the microstructure and crystallite sizes of garnet layers [28].  
In this paper, we investigate the effects of process parameters--in particular, the substrate stage temperature and substrate stage rotation rate--associated with the RF sputter deposition technique, on the properties (stoichiometry, optical, and magneto-optical parameters) of garnet thin films sputtered in a pure argon atmosphere from an oxide-mix-based ceramic target material of composition type Bi\({}_{2.1}\)Dy\({}_{0.9}\)Fe\({}_{3.9}\)Ga\({}_{1.1}\)O\({}_{12}\).