Fabrication and ferromagnetic resonance study of epitaxial spinel ferrite films for microwave device applications
Single crystalline nickel ferrite and lithium ferrite thin films have attracted a lot of research attention recently, because of their unique physical properties for practical applications in next generation technologies, such as monolithic microwave integrated circuits (MMIC) and multiferroic heterostructures. The properties of these materials are closely related to the specific growth method and can be tailored by factors like surface morphology, microstructure and chemical composition. Different thin film growth techniques have been investigated in the past few decades for the fabrication of single crystalline thin films of both these spinel ferrites. However, the difficulty to attain high quality, homogeneous epitaxial films with limited surface and bulk defects and low microwave loss still remains a challenging task. Moreover, there have been very limited reports on the detailed ferromagnetic resonance (FMR) studies of these single crystalline nickel and lithium ferrite thin films, which is an essential aspect to understand the relaxation in magnetization precession (microwave damping) in these materials. In this dissertation work, fabrication and study of structural, magnetic and FMR properties of single crystalline lithium ferrite (LiFe5O8) and nickel ferrite (NiFe2O4) films by direct liquid injection chemical vapor deposition (DLI-CVD) are studied in detail. The growth conditions, which play a crucial role in attaining the desired film morphology and stoichiometry, are optimized to achieve epitaxial, single crystalline lithium ferrite films having low ferromagnetic resonance linewidth coupled with excellent magnetic properties. A detailed ferromagnetic resonance (FMR) study has been done to identify as well as quantify the magnetic relaxation mechanisms in the `as-grown' nickel ferrite films. The broadband frequency, angle and temperature dependent measurements reveal the existence of two-magnon scattering as the active relaxation mechanism for the films.