Structural-controlled chemical synthesis of nanosized amorphous Fe particles and their improved performances

• The amorphous Fe nanoparticles with improved performances have been prepared.
• The fully amorphous Fe nanoparticles with surface B concentration are obtained.
• The alkali reaction solution can promote the formation of amorphous Fe–B phases.
• The amorphous Fe nanoparticles exhibit high saturation magnetization of 138–168 A m2/Kg.

High-performance amorphous Fe nanoparticles with controlled structure and good thermal stability have been fabricated using an optimized chemical method by a direct reduction reaction of Fe2+ ions with NaBH4 as reducing agent. The addition of polyvinylpyrrolidone (PVP) as a surfactant, the properties of solution acidalcaline and the variation of reaction solvent compositions have shown great influences on the morphologies, surface compositions and magnetic properties of the products. The addition of surfactant PVP leads to the formation of fully amorphous Fe nanoparticles. Partial crystallization will occur in the samples prepared without PVP addition and result in their high saturation magnetization up to 168.0 A m2/Kg. The alkali reaction solution with NaOH addition can facilitate the formation of amorphous Fe–B phases in the products instead of the surface B concentration in neutral solution, which promotes their good thermal stability. Reactions in the ethanol-water solvent favor the formation of smaller amorphous iron nanoparticles with about 20 nm in size. The relatively simple chemical synthesis and improved performances including controlled structure, good thermal stability and excellent intrinsic magnetic properties for these amorphous iron nanoparticles promise their potential applications in high-performance multifunctional magnetic devices.