Structure and magnetic properties of Fe(C) and Co(C) nanocapsules prepared by chemical vapor condensation

Abstract

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 Fe 3C when the decomposition temperature is between 500 and 1000 °C, but for 700 °C only Fe 3C exists. α-Fe, γ-Fe and Fe 3C 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 M r/ M s of 0.3–0.4.