Direct Synthesis of Single Crystalline $\alpha$-Fe Nanoparticles With High Saturation Magnetization by Mixed Surfactant

Abstract

Magnetic nanoparticles (NPs) have attracted attention for their potential use in electronic devices and nano-bioengineering applications. Fe NPs made by thermal decomposition from an Fe(CO)x-Oleylamine (OlAm) reacted precursor show high saturation magnetization ( 140 emu/g at 300 K). However, the never reaches to the bulk value (218 emu/g at 300 K) of iron due to the unique crystalline structure of the Fe NPs. Fe NPs coated with OlAm (OlAm-Fe NP) have an expanded (b.c.c.) structure and ultra-fine grains. In this paper, we focus on the adsorption ability of the surfactant to improve via control of phase and grain size. Fe NPs with high saturation magnetization were synthesized by thermal decomposition of Fe(CO) with some surfactants that had weak absorption ability, such as tribenzylamine, trioctylamine, and their mixture. Slow decomposition rate of Fe(CO) and large grain size were obtained by applying surfactants with weak adsorption ability. Especially, Fe NPs that were synthesized by mixed surfactants (mixed surfactant-Fe NPs) have polygonal shape with 6.7 nm in diameter. HRTEM and XRD results suggest that mixed surfactant-Fe NPs are single crystallines of -Fe.of mixed surfactant-Fe NPs is 194 and 183 emu/g at 5 K and 300 K, respectively. These results strongly indicate that single crystallization of -Fe enhances the of Fe NPs and also suggest that optimization of the surfactant adsorption ability is indispensable to promote the single crystallization of Fe NPs.

Oxygen defect assisted paramagnetic to ferromagnetic conversion in Fe doped TiO2nanoparticles

“…We do not completely rule out the possibility of the presence of ferromagnetic clusters or impurities in the doped TiO 2 lattice. However, considering the very high bulk magnetization of Fe (218 emu g À1 ), 37 Fe 2 O 3 (84 emu g À1 ), 38 Fe 3 O 4 (90 emu g À1 ), 39 we could expect at least faint ferromagnetic signal in the samples. But from the observed paramagnetism we can infer that the fraction of Fe or its oxides Fe 2 O 3 , Fe 3 O 4 are too low and most of the Fe ions are in the lattice interior (this is conrmed by the results of EPR).…”

Improvement of saturation magnetization of Fe nanoparticles by post-annealing in a hydrogen gas atmosphere

“…Fe NPs were synthesized by modified thermal decomposition of Fe(CO) 5 -oleylamine reacted precursor. 4 10 ml of Fe(CO) 5 and 25 ml of oleylamine were mixed and kept at 75 C for 1 h, then heated up to 120 C and held for 1 h. 8 ml of the reacted precursor was extracted and injected into 120 ml of dodecane in a three neck flask heated at 200 C. After refluxing for 1 h, the solution was cooled to room temperature and the Fe NPs were separated by magnetic collection and washed with acetone to remove undecomposed precursor and residual surfactant. The Fe NPs were then dried under vacuum at around 1 Pa.…”

“…Fe NPs synthesized by the thermal decomposition of an Fe(CO) 5 -oleylamine reacted precursor have an amorphous-like structure. 5 Therefore, it is reasonable that the M s of these Fe NPs is reduced due to the low crystallinity. However, post-annealing under vacuum caused severe sintering of the Fe NPs before the crystallinity was improved, 6 which also spoiled the uniform diameter distribution.…”

Appearance of Ferromagnetic Property for Si Nanopolycrystalline Body and Vanishing of Electrical Resistances at Local High Frequencies

“…All of them, a method for producing the metal nanoparticles using laser ablation in liquids with high speed and low cost has especially attracted attention [11][12][13][14][15][16][17][18][19]. Many kinds of magnetic nanoparticles [22][23][24][25][26][27][28][29][30][31][32][33][34] (such as Fe [22][23][24][25][26], iron oxides [28], Au [29], Ni [28], and Pd [29][30][31] nanoparticles) have already been researched. Ferromagnetism materials will be applicable to high-frequency core inductors [33][34].…”