Synthesis, structure and dynamic magnetic properties of double-layered Ni-Fe_1−xCo_xhollow microspheres

Abstract

Double-layered Ni-Co1−xFex hollow microspheres with a mean size of ∼1 µm were fabricated by electroless plating of Co or Co-rich CoFe films on Ni hollow spheres (HS); the latter was synthesized by an autocatalytic reaction process. The Ni HS have a microstructure consisting of both fcc and hcp phases and have a very low coercivity. Coating a layer of Co leads to a high coercivity due to the formation of the hcp Co phase with high magnetocrystal anisotropy. Addition of 10% Fe into the Co layer decreases the coercivity from 432 to 140 Oe by transforming the hcp Co phase to the fcc CoFe phase; the latter has a low anisotropy field. Addition of 20% Fe results in a further decrease in coercivity to 69 Oe due to the formation of the bcc CoFe phase. The microwave properties of the composites consisting of HS and a polymer were investigated. Ni HS + a polymer composite have high permittivity but relatively low permeability. Co or CoFe coating decreases the permittivity but slightly increases the permeability of the composite. A reflection loss of <20 dB is obtained for the CoFe coated hollow Ni microspheres with an absorber thickness of 1.5–3.0 mm.

Preparation and microwave absorption properties of electroless Co–P-coated nickel hollow spheres

“…For the composite layers, the maximum attenuation of the incident wave is predicted at the thickness of 3 mm and the value of reflection loss is À36.9 dB. The microwave absorption properties of our samples are better than those of other microspheres with hollow structure reported in literatures [26,29]. When thickness of composite layer increases, the peak of RL moves to lower frequency and becomes narrower.…”

Synthesis, characterization and electromagnetic properties of Fe1−xCox alloy flower-like microparticles

“…The magnetization hysteresis loops all show typical ferromagnetic behavior with coercivity (H C ¼49, 81, and 76 Oe) and high saturation magnetization (M S ¼230, 217, and 214 emu/g) for Fe 1À x Co x (x¼0.4, 0.5, and 0.6) samples, respectively. In general, the coercive force is proportional to the anisotropy field and the higher Co/Fe molar ratio alloy has higher anisotropy field [13]. Hence, with the increase in Co/Fe molar ratio, the H C of Fe 1À x Co x alloys increases.…”

Synthesis of Reusable NiCo@Pt Nanoalloys from Icosahedrons to Spheres by Element Lithography and Their Synergistic Photocatalysis for Nano-ZnO toward Dye Wastewater Degradation

“…Despite recent advances in synthesizing metal hollow nanostructures, such as hollow Pd spheres, hollow PtCo nanoparticles , AuPt bimetallic hollow nanostructures, Co@Au yolk/shell nanospheres, Ni–Fe/Co double-layered hollow spheres, and so on, , there are no reports of trimetallic magnetic-alloy @ noble-metal core–shell hollow nanospheres. On the other hand, the technologically relevant Co–Pt and Ni–Pt systems are important targets, since hollow nanospheres of these alloy systems could find widespread use in magnetic, catalytic, and biomedical applications.…”