Magnetism from intermetallics and perovskite oxides

• Ano de defesa: 2017
• Autor(a) principal: Caraballo Vivas, Richard Javier
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Niterói
• Palavras-chave em Português: Intermetallics; Perovskites; Half-metallic; Magnetocaloric effect; Sample preparation; Perovskita; Magnetismo; Oxidação; Liga metálica; Preparação de amostra; Intermetálicos; Semi-metálico; Efeito magnetocalórico; Preparação de amostras
• Link de acesso: https://app.uff.br/riuff/handle/1/6285

The purpose of this thesis is to elaborate intermetallic alloys and perovskites oxides, in order to understand the magnetic properties of these samples. Specifically, the intermetallic alloys with boron YNi4−xCoxB samples and Co2FeSi and Fe2MnSi1−xGax Heusler alloys were fabricated by arc melting furnace. The sol-gel method was implemented for the synthesis of perovskite oxides of cobalt Nd0.5Sr0.5CoO3 and manganese La0.6Sr0.4MnO3. YNi4−xCoxB was studied in order to explore the magnetic anisotropy originated in 3d sublattice of these samples. Here, we associate the anisotropy with the Co ocupation, due to the non-magnetic nature of yttrium and the non-contribution to the anisotropy of Ni ions. From the ocupation models for Co ions and magnetic measurements, we explained the magnetic behavior of these samples. We develop investigations on structural, magneti and half-metallic properties of Co2FeSi and Fe2MnSi1−xGax Heusler alloys. The Co2FeSi is a promising material for spintronic devices, due to its Curie temperature above 1000 K and magnetic moment lose to 6μB. However, these properties can be influenced by the atomic disorder. Through anomalous X- ray diffraction and Mösbauer spectros copy, we obtained the atomic disorder of the Co2FeSi, and the density functional theory calculations provided information about the influence of the atomic disorder in their half-metallic properties. On the order hand, we also explored the behavior of the magnetic and magneto caloric properties with the increased of the valence electron number in the Fe2MnSi1−xGax Heusler alloys. In addition, we explored the structural and magnetic properties of perovskite oxides of the ABO3 type, mainly the Nd0.5Sr0.5CoO3 cobaltite and La0.6Sr0.4MnO3 manganite. For Nd0.5Sr0.5CoO3, we focus in establishing its spin state configuration, for the Co3+ and Co4+,finding for both intermediate states. Also, we clarfied their intrigue magnetic order, obtaining a ferromagnetic material. The La0.6Sr0.4MnO3 nanoparticles were synthesized in order to explore the effect of size on their properties. We found that the reduction of the nanoparticles size tends to broaden the paramagnetic to ferromagnetic transition, as well as promoting magnetic hysteresis and causing a remarkable change to the magnetic saturation.