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Abstract: Iron carbide Fe3C nanoparticles were fabricated by a chemical vapor condensation (CVC), and their structural and magnetic properties were investigated. It was found that the formation of iron carbide nanoparticles strongly depended on reaction temperature and pressure. The iron carbide was formed only above 650°C at 101kPa (760Torr) but never formed in vacuum (1.33Pa) regardless of reaction temperature. The fabricated iron carbide nanoparticles were spherical with T c of about 240°C. While the particles formed at 650°C (∼30nm) possessed a typical core–shell structure, those formed at 800°C (∼50nm) did not have such structure. The nanoparticles fabricated at 650°C and 800°C at 101kPa, exhibited M s of ∼125Am2/kg whereas i H c of the former was slightly higher (∼63kA/m) than that of the latter (∼40kA/m). [Copyright &y& Elsevier]

Nanosized #x03B5;-Fe3N and iron-nitrides/α-Fe particles with a core-shell structure were prepared by the chemical vapor condensation. Structure and magnetic properties were studied by means of transmission electron microscopy, X-ray photoelectron spectroscopy and vibrating sample magnetometer. The core consists of iron-nitrides/α-Fe or single #x03B5;-Fe3N nanoparticles, while the shell consists of iron oxides. Magnetic properties of #x03B5;-Fe3N nanoparticles can be improved by varying the experimental conditions. The maximum value of the saturation magnetization reaches 126.1 emu/g for the #x03B5;-Fe3N nanoparticles prepared at 1000°C by a pure 60 sccm NH3 carrier gas. [Copyright &y& Elsevier]

Carbon-coated cobalt nanocapsules were synthesized by the chemical vapor-condensation process with cobalt carbonyl (Co2(CO)8) used as precursor and carbon monoxide (CO) as carrier gas. The characterization and magnetic properties of carbon-coated cobalt nanocapsules were investigated systematically. The transmission electron microscope (TEM) images showed that the as-prepared nanoparticles consist of a metal core and an amorphous carbon shell. X-ray diffraction and TEM selected area diffraction revealed the presence of f.c.c. Co phase, h.c.p. Co phase, and minority Co2C, Co3C phases. The saturation magnetization at room temperature of the nanocapsules is 146.9 Am2 kg−1, which is 90% of the bulk ferromagnetic element counterpart. The coercive force at room temperature of the nanocapsules is 0.12 T, while the ratio of remnant to saturation magnetization Mr/Ms is about 0.4. The saturation magnetization and the coercive force increase with increasing the decomposition temperature, mainly due to the increase of the size of the magnetic particles. The decomposition of the cobalt carbonyl (Co2(CO)8) and CO gas can decrease efficiently the oxygen content in nanocapsules. The metallic Co nanoparticles completely coated by carbon can resist the dilute acid erosion as well as the oxidation. The thermal stability of the Co nanocapsules is also studied. [Copyright &y& Elsevier]

Fe–Co nanoparticles were synthesized by the chemical vapor condensation process using the organometallics as precursors under a flowing helium atmosphere. The relations between the resulting microstructure, magnetic properties and the process parameters were investigated. The crystalline structure after oxidation at different temperatures was analyzed. The mean size of the Fe–Co nanoparticles increases with increasing the decomposition temperature. The saturation magnetization increases with increasing the particle size. The maximum value of the coercivity reaches up to 1739 Oe for the Fe–Co nanoparticles oxidized at 400 °C. [Copyright &y& Elsevier]

Abstract: ε-Fe3N nanoparticles synthesized by chemical vapor condensation (CVC) are covered with shells of disordered Fe3O4 phase, as observed by a transmission electron microscopy. The zero-field cooling and field cooling temperature dependence of magnetization, ac susceptibility as a function of frequency, magnetic hysteresis loops, and the temperature dependence of resistivity of the ε-Fe3N nanoparticles are systematically studied. The results indicate the existence of complex magnetic properties, such as superparamagnetic behavior, exchange bias, magnetic dipole interaction, and the possible coexistence of ferromagnetic and spin-glass-like states and/or disordered surface spins of the shells at low temperatures. The temperature dependence of resistivity ρ(T) for compacted ε-Fe3N nanoparticles in a temperature range of 110K

Nanocrystalline α-Fe and #x03B5;-Fe3N particles were synthesized by chemical vapor condensation method using Fe(CO)5 in a flowing NH3 atmosphere. Structural characteristics were investigated systematically by means of X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive X-ray. The mean particle size was in the order of 10–40 nm with uniform dispersion. With increasing decomposition temperature, the phase transformation occurred from amorphous+α-Fe nanoparticles to amorphous +α-Fe + Fe–N nanoparticles, and then to #x03B5;-Fe3N nanocrystalline. Magnetic properties of the Fe–N nanocrystalline particles were examined by vibrating sample magnetometer. [Copyright &y& Elsevier]

Carbon-coated Fe and Co nanocapsules have been synthesized by a chemical vapor condensation process using carbon monoxide as carrier gas. The characterization and magnetic properties of carbon-coated Fe and Co nanocapsules are investigated and compared. The core/shell structure of the Fe(C) nanocapsules is similar to that of the Co(C) nanocapsules, consisting of an amorphous shell and a metallic core. The phases of the Co(C) nanocapsules are composed of f.c.c.-Co, h.c.p.-Co and cobalt carbides regardless of the decomposition temperature and the CO gas flow rate. The phases of the Fe(C) nanocapsules change with changing decomposition temperature and CO gas flow rate. The majority phases of the Fe(C) nanocapsules are α-Fe and Fe3C when the decomposition temperature is between 500 and 1000 °C, but for 700 °C only Fe3C exists. α-Fe, γ-Fe and Fe3C phases coexist after preparation at 1100 °C. The saturation magnetization of the Co(C) nanocapsules increases with increasing decomposition temperature, while that of the Fe(C) nanocapsules is less dependent on the phases formed. The cobalt nanocapsules reach 90% of the value of the saturation magnetization of bulk cobalt, while the iron nanocapsules obtained at 400 and 1100 °C reach 75 and 33% of the saturation magnetization of bulk iron. The carbon-coated Fe and Co nanocapsules are shown to be ferromagnetic with a ratio of the remnant magnetization to saturation magnetization Mr/Ms of 0.3–0.4. [Copyright &y& Elsevier]