Iron garnets (IGs) are materials with unique radio-frequency (rf) properties. They are already being used as GHz oscillators, magneto-optical filters, and circulators. Recently used growth methods, including the rf sputtering technique, now allow the fabrication of nm-thick films and multilayers, compatible with lithography techniques for device fabrication. In some cases (two-step growth), IGs fabricated using physical vapor deposition techniques are crystallized following deposition at room temperature. This work focuses on an in situ structural characterization of IGs during the annealing process to determine the crystallization mechanism and dynamics. It is found that IG crystallization leads to heteroepitaxy but the crystallized thickness does not grow linearly with time and competes with diffusion from the substrate. Modeling the crystallization dynamics demonstrates a two-dimensional solid phase epitaxy (SPE) mechanism using a Johnson-Mehl-Avrami-Kolmogorov approach. This SPE is controlled by interface nucleation, and differs from the expected one-dimensional SPE from the interface to the surface considered before. The determined crystallization and diffusion activation energies are in agreement with the ones found in the literature. The obtained results allow us to find the best compromise between annealing time and temperature needed for IG crystallization in order to minimize the effect of substrate diffusion, especially Gd magnetic atoms, which are detrimental to the IG rf quality factor.

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• Crystal growth
• Crystal phenomena
• Magnetism
• Crystalline systems
• Annealing
• Crystallization
• Epitaxy
• X-ray diffraction
• X-ray reflectivity