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Anisotropic cobalt-based nanostructures: synthesis and characterization
Different types of cobalt-based magnetic nanoparticles have been designed to im-prove their performances in modern applications. For example, 3d transition metal-based magnetic nanowires are currently considered as potential candidates for rare-earth-free permanent magnets and for applications in catalysis. This thesis describes possible ap-proaches for the design of optimized architectures on the nanoscale exploiting the combi-nation of shape, magnetocrystalline and exchange anisotropy in 3d-metals. First, in a novel approach for the magnetic hardening, electroplated Fe30Co70 nanowires in anodic alumi-num oxide templates with diameters of 20 nm and 40 nm (length 6 μm and 7.5 μm, re-spectively) are synthesized and thoroughly characterized by structural and magnetic tech-niques. A 3–4 nm thick, naturally formed ferrimagnetic FeCo oxide layer covering the tip of the FeCo nanowire increases the coercive field by 20% at T = 10 K. The increase of the coercive field is achieved by means of magnetic pinning by an antiferromagnet which suppresses vortex formation at the tips of the nanowires as suggested by micromagnetic simulations. Second, Co80Ni20 nanorods with a mean diameter of 7 nm and a mean length of 53 nm have been synthesized by colloidal chemistry using the polyol process. Structural anal-ysis shows crystalline rods with the crystallographic c-axis of the hexagonal close-packed (hcp) phase, i.e. the magneto-crystalline easy axis, parallel to the long axis of the Co80Ni20 alloy rods. Moreover, these are covered by a thin Co-rich oxidized face-centered cubic (fcc) shell. This shell promotes a larger hysteretic energy product by exchange anisotropy between the antiferromagnetic oxide shell and the ferromagnetic metallic core. In a third study, cobalt oxide nanoparticles have been examined having a good cata-lytic response and additional magnetic properties. A new synthetic procedure has been developed to master the magnetic properties of cobalt oxide nanocrystals. 20 nm, 40 nm, and 85 nm edge length CoO-Co3O4 ...
Anisotropic cobalt-based nanostructures: synthesis and characterization
Different types of cobalt-based magnetic nanoparticles have been designed to im-prove their performances in modern applications. For example, 3d transition metal-based magnetic nanowires are currently considered as potential candidates for rare-earth-free permanent magnets and for applications in catalysis. This thesis describes possible ap-proaches for the design of optimized architectures on the nanoscale exploiting the combi-nation of shape, magnetocrystalline and exchange anisotropy in 3d-metals. First, in a novel approach for the magnetic hardening, electroplated Fe30Co70 nanowires in anodic alumi-num oxide templates with diameters of 20 nm and 40 nm (length 6 μm and 7.5 μm, re-spectively) are synthesized and thoroughly characterized by structural and magnetic tech-niques. A 3–4 nm thick, naturally formed ferrimagnetic FeCo oxide layer covering the tip of the FeCo nanowire increases the coercive field by 20% at T = 10 K. The increase of the coercive field is achieved by means of magnetic pinning by an antiferromagnet which suppresses vortex formation at the tips of the nanowires as suggested by micromagnetic simulations. Second, Co80Ni20 nanorods with a mean diameter of 7 nm and a mean length of 53 nm have been synthesized by colloidal chemistry using the polyol process. Structural anal-ysis shows crystalline rods with the crystallographic c-axis of the hexagonal close-packed (hcp) phase, i.e. the magneto-crystalline easy axis, parallel to the long axis of the Co80Ni20 alloy rods. Moreover, these are covered by a thin Co-rich oxidized face-centered cubic (fcc) shell. This shell promotes a larger hysteretic energy product by exchange anisotropy between the antiferromagnetic oxide shell and the ferromagnetic metallic core. In a third study, cobalt oxide nanoparticles have been examined having a good cata-lytic response and additional magnetic properties. A new synthetic procedure has been developed to master the magnetic properties of cobalt oxide nanocrystals. 20 nm, 40 nm, and 85 nm edge length CoO-Co3O4 ...
Anisotropic cobalt-based nanostructures: synthesis and characterization
2016-02-12
Theses
Electronic Resource
English
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