Spontaneously Formed Interfacial Metal Silicates and Their Effect on the Magnetism of Superparamagnetic FeCo/SiO₂ Core/Shell Nanoparticles

Abstract

The integration of superparamagnetic core/shell nanoparticles into devices and other nanoscale technological applications requires a detailed understanding of how the intimate contact between core and shell nanophases affects the magnetism. We report how, for single-domain FeCo nanoparticles, an FeCo phase unique to the nanoscale with silica shells of increasing thicknesses spontaneously formed interfacial metal silicates between the core and shell (such as Fe2SiO4 and Co2SiO4) and altered the overall magnetism of the nanomaterial significantly. The influence of this previously overlooked phenomenon on magnetic properties is reported. Evidence of these metal silicate interfacial layers was observed by X-ray absorption spectroscopy (XAS) collected over the L3,2 absorption edges of Fe and X-ray photoelectron spectra (XPS) collected over the 2p transitions of Fe and Co. Through the correlation of magnetometry and XPS data, the evolution of nanoparticle magnetic anisotropy is shown to increase with the metal silicate.

Unraveling The Origin of Enhanced Field Emission from Irradiated FeCo-SiO2Nanocomposites: A Combined Experimental and First-Principles Based Study

“…Since the role of insulating matrix is to restrict the heat flow inside metal NPs to cause a sharp rise in temperature inside the same for reaching a molten state, we have confined our calculations to FeCo metal clusters only. However, silicate phases are likely to be present at the interface of NPs and SiO 2 matrix . In the present study, we have ignored the effect of SiO 2 –NPs interface mixing and have first modeled a nanocluster of (FeCo) 8 without the SiO 2 matrix.…”

Facile synthesis of a CNT@Fe@SiO2 ternary composite with enhanced microwave absorption performance

“…The silica oxide coating of CNT@Fe was produced via a modi-ed Stober method. 30,31 Typically, 200 mg of the CNT@Fe sample was dispersed in a mixture of 80 mL of distilled water, 20 mL of absolute ethanol and 2 mL of ammonium. Next, every 30 min, 0.5 mL of TEOS (total of 4 mL) was dropped into the mixed solution.…”

Improving Powder Magnetic Core Properties via Application of Thin, Insulating Silica-Nanosheet Layers on Iron Powder Particles

“…An insulating layer composed of sodium salts has a high thermal resistance and can be formed homogeneously, but pure iron is prone to corrosion by sodium salts. Of the various insulating materials used for magnetic materials, silica provides excellent stability against corrosion, oxidation, and a high thermal-resistance [ 22 , 23 , 24 , 25 , 26 ]. Silica coating of magnetic powder particles is often carried out via the hydrolyzation of tetraethoxysilane (TEOS), but this method makes it difficult to achieve thin, homogeneous layers of silica [ 19 , 20 , 21 , 22 , 23 ].…”