Fabrication and Characterization of Ce:YIG Thin Films with Sub-Micron Magnetic Domains for Advanced Magnetooptical Devices

In the realm of magneto-optics and spin photonics, researchers are increasingly interested in optical devices that leverage magnetic materials, particularly those exhibiting nano to microscale magnetic domains. These innovative devices encompass a range of applications, from photonic integrated circuits and advanced 3D displays to holographic storage systems, high-power Q-switched lasers, random number generators, and optical computing components. Central to these advancements are magnetooptical materials that can maintain nanoscale magnetic domains while demonstrating substantial magnetooptical effects and high transparency [1]. To tackle this challenge, our research centered on cerium-substituted yttrium iron garnet (Ce:YIG) films, aiming to create films with strong perpendicular magnetic anisotropy using ion beam sputtering techniques.<br/>We deposited a 130 nm thick film of Ce:YIG on a gadolinium gallium garnet (GGG) substrate using radio-frequency ion beam sputtering (RF-IBS). During deposition, the substrate was maintained at 810 °C and rotated to ensure uniform film growth [2]. We confirmed the film's high crystallinity and structural integrity through X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses.<br/>Using a Faraday effect microscope with a 470 nm laser source, we observed maze-shaped magnetic domains. These domains measured about 300 nm in width, with domain walls estimated to be approximately 50 nm wide. Vibrating-sample magnetometry (VSM) verified perpendicular magnetic anisotropy with an anisotropy energy of roughly 13.7 kJ/m³ and a saturation magnetization of 130 emu/cm³. The film exhibited a Faraday rotation angle of -1.1 °/µm at 1064 nm. X-ray photoelectron spectroscopy (XPS) showed that the electronic state of cerium was predominantly Ce³⁺.<br/>We employed computational modeling using high-performance parallel computing to simulate the magnetic domain state in a 5 x 5 x 0.12 µm³ volume with a 10 x 10 x 10 nm³ cell size. The simulation produced domain sizes of about 150 nm and domain walls of approximately 50 nm. While the experimental and computational results differed in scale, both demonstrated maze-like patterns, validating the model's accuracy.<br/>These findings underscore the potential of RF-IBS-created Ce:YIG thin films for applications such as magnetooptical recording, holographic media, and high-power Q-switched lasers. The combination of perpendicular magnetic anisotropy, sub-micron maze-shaped domains, and high Faraday rotation makes these films promising candidates for further magnetooptical applications.<br/>[1] T. Goto, et al., Opt. Express 24, (2016) 17635.<br/>[2] Y. Yoshihara, et al., Appl. Phys. Lett. 123(11), 112404 (2023).