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.
The magnetic properties of Fe nanoparticle-based bulk material, which was fabricated with a through post-annealing process under vacuum conditions, were investigated to develop a new Fe-based soft magnetic material. Fe nanoparticles (NPs) retained uniform-size and narrow-size distributions at a post annealing temperature (Ta) of 473K. Their assembly was self organized, which is referred to as nano size periodicity. Soft magnetic properties were obtained at 1.7±0.2 Oe of coercivity at room temperature, and 179 emu/gnet of saturation magnetization was obtained at 5K by using Ta=473 K. Above Ta= 573 K, saturation magnetization decreased and coercivity was increased. High temperature post-annealing above 523 K caused NP growth and the transformation α-Fe to Fe 3 C, which originated from carbon impurities in the surfactant. Thus, the low-temperature post-annealing process plays an important role in achieving high performance soft magnetic properties using Fe NP-based bulk material by desorbing of surfactants without the formation of iron carbide.
Magnetic nanoparticles (NPs) have attracted attention for their potential use electronic devices and nano-bioengineering applications. Fe NPs made from an Fe(CO) x-Oleylamine (OlAm) reacted precursor by thermal decomposition show high saturation magnetization (σ s) (~140 emu/g net at 300 K). However, the σ s never reaches the bulk value (218 emu/g at 300 K) of iron. This is due to the unique crystalline structure of the Fe NPs. Fe NPs covered with OlAm (OlAm-Fe NP) have an expanded α(b.c.c.) structure and ultra-fine grains. We improved the σ s of Fe NPs via phase control by adjusting the adsorption ability of a surfactant such as trioctylamine (TOcAm) or tribenzylamine (TBeAm). These surfactants have weaker adsorption ability than that of OlAm. Rietveld analysis revealed that the crystalline structure of Fe NPs covered with TOcAm or TBeAm was drastically changed into a rather α-Fe phase, in contrast to the expanded α phase observed for the OlAm-Fe NPs. TOcAm-Fe NPs had 10-80 vol.% of the α-Fe phase, and TBeAm-Fe NPs had 80-99 vol.% of the α-Fe phase, which indicates an α-Fe single phase. A σ s of 199 emu/g net for the TBeAm-Fe NPs was obtained at 300 K. This remarkable improvement is due to the increase volume fraction of the α-Fe phase. These results suggest that α-Fe phase formation using weak adsorption surfactant was highly effective for improving the σ s .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.