Publicação
Nanostructured rare-earth free permanent magnets
| Resumo: | In this work we explore on the rare-earth free nanostructured permanent magnets, including thin films, nanoparticles and nanocomposites with the focus on Alnico magnets and hexaferrites. Here we investigate the effects of different heat treatment conditions on structural and magnetic properties of RFsputtered Alnico V thin films on Si substrates. We show an in-depth analysis of the various heat treated samples with high coercivity to unveil the origin of high coercivity in these thin films with a recently discovered Fe-Co rich Body- Centered Tetragonal (bct) phase. Exchange-spring magnets are also explored, namely barium hexaferrite (BaM) and strontium hexaferrite (SrM). We investigate on the possibility of coating BaM and SrM flake-like hexaferrite particles via a hydrothermal and coprecipitation method to prepare core-shelllike BaM/Fe3O4 and SrM/Fe3O4 nanocomposites, where the ferrite particles where prepared via a sol-gel auto-combustion method. We show how optimised hard to soft magnetic phase ratio and preparation conditions lead to a significant enhancement in their hard magnetic properties compared to commercial ferrite powders. Moreover, we employ the prepared highperformance exchange-coupled nanocomposite powder and investigate the mechanical and magnetic properties of warm compressed nanocomposite powder in an epoxy matrix. We show how the powder-to-resin ratio and preparation conditions lead to optimised mechanical properties, and enhancement in the maximum energy product of the composite magnet. Finally, micromagnetic simulations were employed to better understand and support the experimental results of the exchange coupling behaviour of the BaM/Fe3O4 hard-soft magnetic nanocomposites. We show how the thickness of BaM particles affect their coercivity and how the volume fraction of each magnetic phase, together with their interface area, affect the exchange coupling behaviour and maximum energy product of the nanocomposite magnets. |
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| Autores principais: | Mohseni, Farzin |
| Assunto: | Rare-earth free permanent magnets Sputtering Alnico BaFe12O19 SrFe12O19 Hexagonal ferrite Magnetite Fe3O4 Magnetic exchange coupling Nanocomposite hard magnets Exchange-spring magnets Warm compaction Polymer bonded magnets Micromagnetism Mumax3 simulations |
| Ano: | 2021 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | In this work we explore on the rare-earth free nanostructured permanent magnets, including thin films, nanoparticles and nanocomposites with the focus on Alnico magnets and hexaferrites. Here we investigate the effects of different heat treatment conditions on structural and magnetic properties of RFsputtered Alnico V thin films on Si substrates. We show an in-depth analysis of the various heat treated samples with high coercivity to unveil the origin of high coercivity in these thin films with a recently discovered Fe-Co rich Body- Centered Tetragonal (bct) phase. Exchange-spring magnets are also explored, namely barium hexaferrite (BaM) and strontium hexaferrite (SrM). We investigate on the possibility of coating BaM and SrM flake-like hexaferrite particles via a hydrothermal and coprecipitation method to prepare core-shelllike BaM/Fe3O4 and SrM/Fe3O4 nanocomposites, where the ferrite particles where prepared via a sol-gel auto-combustion method. We show how optimised hard to soft magnetic phase ratio and preparation conditions lead to a significant enhancement in their hard magnetic properties compared to commercial ferrite powders. Moreover, we employ the prepared highperformance exchange-coupled nanocomposite powder and investigate the mechanical and magnetic properties of warm compressed nanocomposite powder in an epoxy matrix. We show how the powder-to-resin ratio and preparation conditions lead to optimised mechanical properties, and enhancement in the maximum energy product of the composite magnet. Finally, micromagnetic simulations were employed to better understand and support the experimental results of the exchange coupling behaviour of the BaM/Fe3O4 hard-soft magnetic nanocomposites. We show how the thickness of BaM particles affect their coercivity and how the volume fraction of each magnetic phase, together with their interface area, affect the exchange coupling behaviour and maximum energy product of the nanocomposite magnets. |
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