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Abstract:
Modern development of information technologies such as memory storages and logic operations demands for faster, denser, non-volatile and low power-consuming technologies. This has driven significant research in the area of spintronics, or spinelectronics, which is based on the idea of exploiting both the charge and spin degrees of freedom of the electron. A key focus in this field is on ferrimagnetic oxides, in particular Rare-earth Iron Garnets (ReIG). These materials show great potential for use in insulator-based magnetic devices that generate pure spin currents. ReIGs exhibit unique magnetic properties, making them promising candidates for insulator spintronics applications, including skyrmion stabilization and spin wave propagation. These applications, however, require the fabrication of nanometer-thick garnet films.
In this work, we optimized the fabrication of epitaxial thin films of ReIG, in particular YIG and perpendicularly magnetized TmIG. This was performed via radio frequency sputtering technique and post-annealing, allowing to obtain high quality epitaxial ultrathin films down to 3 nm. The heteroepitaxial structure and crystalline quality of the fabricated films was confirmed with X-ray measurements. The in-situ measurements of ReIGs during the annealing process were performed as well, which allowed us to determine the crystallization dynamics separated in two simultaneous phases: garnet crystallization and diffusion. It was determined that the ReIGs crystallization phase is not linear, and the modeling of the process using Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach was developed, with the correction to the diffusion process from the substrate to the garnet layer.
The magnetic properties of ReIGs were studied and, in order to optimize them to stabilize smaller magnetic textures like stripe domains or bubbles, several ways of reducing effective anisotropy were investigated. Two of them, including the optimization of the annealing parameters and the fabrication of YIG/TmIG bilayers with different easy magnetization axis, turned out to be quite efficient. This allowed us to tune the effective anisotropy to stabilize stripe domains and magnetic bubbles at remanence. The studies of the ReIG magnetization dynamics demonstrated that its properties highly depend on the garnet composition, and, therefore, on the fabrication process and the annealing procedure conditions. An optimum of these constrains was found allowing to preserve the low damping of ReIGs.
The synchrotron studies of ReIGs demonstrated the difference in the garnet composition between the layer at the interface and the surface and confirmed the presence of a non-magnetic layer, created due to the substrate diffusion into the garnet layer. This effect was observed during the crystallization studies, and the approximate thickness of this layer ≈ 2 nm was determined from both hard and soft X-ray measurements
