Synthesis and characterization of core-shell structure silica-coated Fe29.5Ni70.5 nanoparticles

TL;DR

This paper presents a novel ultrasound-assisted synthesis method for creating silica-coated FeNi nanoparticles with a core-shell structure, maintaining magnetic properties and demonstrating potential for biomedical and electromagnetic applications.

Contribution

It introduces an ultrasound-enhanced Stober method for uniform silica coating of FeNi nanoparticles, preserving magnetic properties and controlling shell thickness.

Findings

Silica coating does not alter core magnetic properties.

Particles remain ferromagnetic at 77 K and room temperature.

Coercive force varies non-monotonously with silica layer thickness.

Abstract

In view of potential applications of magnetic particles in biomedicine and electromagnetic devices, we made use of the classical Stober method base-catalysed hydrolysis and condensation of tetraethoxysilane (TEOS) to encapsulate FeNi nanoparticles within a silica shell. An original stirring system under high power ultrasounds made possible to disperse the otherwise agglomerated particles. Sonication guaranteed particles to remain dispersed during the Stober synthesis and also improved the efficiency of the method. The coated particles are characterized by electron microscopy (TEM) and spectroscopy (EDX) showing a core-shell structure with a uniform layer of silica. Silica-coating does not affect the core magnetic properties. Indeed, all samples are ferromagnetic at 77 K and room temperature and the Curie point remains unchanged. Only the coercive force shows an unexpected non-monotonous dependence on silica layer thickness.