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Using a wet chemical method, we have synthesized chain-like structure with diameters of 200-250 nm and lengths of approximately 10 microm formed by assembly of small cobalt nanoparticles. The chain-like structures were realized via reaction of CoCl2 x 6H2O and N2H4 in the presence of PVP in an ethylene glycol solution. Magnetic measurements show a coercivity of about 122 Oe at 300 K. We also propose a possible mechanism for the formation of the chain-like structures.

Polycrystalline magnetite hollow spheres with diameter of about 200 nm and shell thickness of 30-60 nm were prepared via a facile solution route. For the reaction, ethylene glycol (EG) served as the reducing agent and soldium acetate played the role of precipitator. In addition, polyvinylpyrrolidone (PVP) served as a surface stabilizer. The morphologies and structures were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The intermediate products at different stages were also studied to shed light on the evolution of phase formation. It revealed that the hollow structure formed via self-assembly of nanocrystallites (about 15 nm) using sodium acetate as mild precipitator. Evidences further pointed out that the Ostwald ripening process well explained the growth mechanism of the hollow structure. Magnetization measurements showed that the coercivity of magnetite hollow spheres at low temperature is about 200 Oe and the saturation magnetization is about 83 emu g, roughly 85% that of the bulk phase, close to the value of its solid counterpart. In addition, a freezing transition was observed at 25 K. [ABSTRACT FROM AUTHOR]

Using a one-step solution phase approach, the authors have synthesized uniform jingle bell-shaped cobalt mesopheres (550–750 nm) and assembled the mesospheres into long magnetic chains (20–30 μm). All of the cobalt spheres are hollow with ∼40 nm thick shells but each contains an ∼200 nm diameter solid ball. The nano- to mesoscale structures were realized via reaction of CoCl2·6H2O and N2H4·H2O in the presence of polyvinylpyrrolidone (PVP) in an ethylene glycol solution. Magnetic measurements show a coercivity of about 75 Oe with a remnance of 9.6 emu/g at 300 K. We propose a possible mechanism for the formation of the nanoto mesoscale structures. [ABSTRACT FROM AUTHOR]