Synthesis and Stabilization of FeCo Nanoparticles

Synthesis of high magnetic moment CoFe nanoparticles via interfacial diffusion in core/shell structured Co/Fe nanoparticles

“…Magnetic studies were carried out using a Lakeshore 7404 highsensitivity vibrating sample magnetometer (VSM) with magnetic fi eld up to 1.5 T at room temperature. The wt% of metals in the NPs was obtained by measuring the weight difference before and after annealing the particles in a thermogravimetric analysis (TGA) pan at 800 °C under Ar for 1 h. [7,11,12], controlled alloying of Co and Fe in a single NP with tunable Co and Fe composition is still a challenging goal in synthesis. It is diffi cult to fi nd Co and Fe precursors with chemical properties that have similar thermodynamics and growth kinetics under the same growth conditions.…”

“…However, the chemical instability of nanostructured CoFe has made the synthesis of robust high magnetic moment CoFe NPs extremely challenging. Recent advances in NP syntheses have indicated that solution phase chemical synthesis is a reliable process for producing various monodisperse magnetic NPs by either simultaneous decomposition of Co( 3 -C 8 H 13 )( 4 -C 8 H 12 ) (or Co(N(SiMe 3 ) 2 ) 2 ) and Fe(CO) 5 [11], or co-reduction of Co(acac) 2 and Fe(acac) 3 (acac = acetylacetonate) [12]. However, CoFe NPs made by these processes are chemically unstable, being subject to fast oxidation into various oxides unless a chemically inert carbonaceous shell is coated under high-temperature reaction conditions [7].…”

First-principles prediction of enhanced magnetic anisotropy in FeCo alloys

“…It has been shown that the replacement of a soft phase ͑K 1 =0͒ by a suitably aligned semihard phase ͑0 Ͻ K 1 Ͻ K h ͒ is beneficial in permanent-magnet nanostructuring 2-4 but the challenge is to find semihard materials that combine moderate anisotropy with a high magnetization. Traditional Fe 1−x Co x alloys are ideal candidates for hard-soft nanostructuring 5,6 because they have a very high magnetization in a wide range of Fe-rich compositions. However, their anisotropy is typically very low ͑K s ϳ 0͒ or its development requires a huge and difficultto-realize tetragonal strain c / a ϳ 1.2.…”

Superparamagnetic Nanoparticles as High Efficiency Magnetic Resonance Imaging T2 Contrast Agent

“…14 Chemical reduction of metal ions by sodium borohydrides has previously been used to prepare nanocrystalline magnetic materials, nanoalloys, and amorphous metals. 34,35 In this work, we report a new two-step synthesis to prepare magnetoresponsive gold/iron nanoparticles (Au/Fe NPs) with two mixed-ligand coatings, either mercaptopropionylsulfonic acid:-o c t a n e t h i o l ( M P S A : O T ) o r m e r c a p t o u n d e c y lsulfonate:octanethiol (MUS:OT). Structural characterization and elemental analysis demonstrate that the resulting bimetallic nanoparticles have an average diameter of 4 nm (MPSA:OT, 4.0 ± 1.3 nm; MUS:OT, 4.0 ± 1.0 nm) with an average atomic ratio of Au to Fe of 7 (MPSA:OT) and 8 (MUS:OT), which enables Au/Fe NPs to be superparamagnetic at room temperature, with a blocking temperature of 56 K (MPSA:OT) and 96 K (MUS:OT), depending on the coating.…”