Structure and magnetic properties of iron nanoparticles stabilized in carbon

Abstract

Nanoparticles composed of iron and carbon have been produced by chemical vapor synthesis. A detailed structural, electronic, and magnetic characterization has been performed by several methods. The atomic arrangement in the as-prepared particles is strongly affected and stabilized by excess carbon. Small clusters of different ferrous phases are the building blocks of the particles. Due to the in situ formation of a carbonaceous shell the particles are stable against oxidation at ambient conditions. The magnetic properties are influenced by the exceptionally small particle size. The particles exhibit superparamagnetic behavior with a blocking temperature of 30K and the temperature dependence of the magnetization is governed by the finite size of the system.

Onion-like nanoparticles with γ-Fe core surrounded by a α-Fe/Fe-oxide double shell

“…In the case of Fe@AC NPs, ferromagnetic (FM) Fe-NPs and ferrimagnetic (FIM) Fe-oxides, successfully synthesized within different protecting coatings and/or matrices, have been largely studied ( [1][2][3][8][9][10][11] and references therein). However, ␥-Fe NPs have received less attention [10,[12][13][14]. The main reason for that is the difficulty for stabilizing the high temperature (above 1180 K) stable phase of iron, ␥-Fe, with face-centered cubic (FCC) crystal structure.…”

Microstructure and magnetism of nanoparticles withγ-Fecore surrounded byα-Feand iron oxide shells

“…This high relative percentage of ␥-Fe and the good signal vs noise relationship allow us an exhaustive study of this striking crystalline phase and stress the importance of the followed synthesis procedure among others that only provides small amounts of ␥-Fe. 49 It has been mentioned that the last step of the synthesis route ͑see Sec. II͒ consisted in exposing the sample to air in order to stabilize the Fe-NPs.…”

“…Up to now, this ␥-Fe phase was observed in small iron precipitates embedded in a Cu matrix, 38 in FeCu mechanically alloyed compounds, 39,40 in the synthesis of carbon nanotubes, [41][42][43][44][45][46][47][48] or in Fe-NPs and thin films but confined down to a few monolayers of thickness. [49][50][51][52][53][54][55] The magnetism of ␥-Fe phase depends strongly on the Fe-Fe interatomic distances 56 although both the morphology of the sample and the particle size could play an important role. Indeed, AFM interactions are favored at low temperatures ͑T Ͻ 100 K͒ and for lattice parameters, a Ͻ 3.6 Å, while FM state with high Fe magnetic moment values ͑ Ͼ 2.5 B ͒ can be stabilized for a Ͼ 3.6 Å.…”

Synthetic Techniques and Applications of Activated Nanostructurized Metals: Highlights up to 2008

“…(2) and consists of a horizontal furnace with a quartz tube (with a 2.2 cm internal diameter, and 2.5 cm external diameter) as the reaction chamber in which controlled flows of argon and hydrogen can be introduced directly via a bubbler with the desired liquid as the carbon source. The CVD has been used for obtaining generally carbon nanoparticles described elsewhere; however, some pure metallic nanoparticles can also be prepared this way, for instance Fe [58][59][60], W, Mo, Al, Au, Cu, and Pt [61]. Palladium (Pd) nanoparticles are incorporated into free-standing polymer films by a one-step dry process involving simultaneous vaporization, absorption and reduction schemes of palladium(II) bis(acetylacetonate), Pd(acac) 2 , used as a precursor [62].…”