Caracterização estrutural e magnética de filmes finos de Gd depositados por magnetron sputtering

• Ano de defesa: 2023
• Autor(a) principal: Bernardino, Simone Venturim
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Espírito Santo; BR; Doutorado em Física; Centro de Ciências Exatas; UFES; Programa de Pós-Graduação em Física
• Palavras-chave em Português: Filme fino; Gadolínio; Magnetron Sputtering; Orientação cristalina; Anisotropia magnética; Física
• Link de acesso: http://repositorio.ufes.br/handle/10/12683

Initially, the structural and magnetic properties of thin gadolinium films with thicknesses of 20, 50 and 200 nm grown by a Magnetron Sputtering on (100) silicon substrate at room temperature have been investigated. Thus, among the three samples, the 200 nm thin gadolinium film excelled since it only presents a compact hexagonal phase with a strong preferential orientation of the (002) planes, higher Curie temperature value and higher saturation magnetization (55% higher than that obtained with a thickness of 50 nm). Therefore, the thickness of the deposited thin films was kept constant in 200 nm to study the changes of properties of the gadolinium films caused by the variation of the following growing experimental conditions: substrate temperature and application of the bias sputtering procedure before the deposition of the materials. A 3 nm thick platinum protective layer has been deposited on all gadolinium films to avoid the surface oxidation. The samples produced at 300 K or 673 K presented only the compact hexagonal phase or two polymorphic crystalline structures (compact hexagonal and face-centered cubic), respectively. In details, with increasing substrate temperature during the deposition, from 300 K to 673 K, it was found that: (i) the crystals of the compact hexagonal phase had their axes of crystalline symmetry preferentially reoriented from the perpendicular to the parallel direction to the film plane; (ii) it occurred the appearance of the face-centered cubic structure with (111) planes preferentially parallel to the film plane and (iii) there was an increase of the dispersion of the crystallite orientations for the two polymorphic structures. The samples showed thermal hysteresis of (6 ± 1) K close to room temperature as a consequence of the magnetocaloric effect. The analysis of the ferromagnetic resonance results showed that an in-plane magnetization is favored by the face-centered cubic phase and the (100) preferential crystalline orientation of the compact hexagonal structure. Finally, these results suggest that internal strains in the films can induce reorientation of crystalline axes and the appearance of the face-centered cubic phase, factors that can strongly influence the effective anisotropy of the thin film and make the magnetic analysis more complex, when compared to what occurs in the macroscopic dimension. This study brings new approaches to the structural and magnetic properties of gadolinium thin films that have aroused the interest of the scientific community in recent decades due to their application in magnetocaloric refrigerators, high resistance alloys, permanent magnets and magnetic resonance imaging contrast agents.