Influence of Al on synthesis and properties of carbon-encapsulated iron nanoparticles

• Inclusion of Al narrows diameter distribution.
• Content of paramagnetic fcc Fe–C phase increases with increase of Al content.
• Inclusion of Al lowers saturation magnetization.
• Growth of carbon-encapsulated iron nanoparticles is a non-equilibrium process.

Each method of encapsulation of Fe nanoparticles in carbon coatings results in formation of thermodynamically unstable austenite phase. The presence of austenite is highly unwanted because it drastically worsens the magnetic performance of carbon-encapsulated iron nanoparticles. This paper verifies whether the inclusion of Al, which is known as efficient ferrite stabilizing element, may eliminate this unwanted paramagnetic phase in carbon-encapsulated iron nanoparticles synthesized via carbon arc discharge route. The influence of Al on the synthesis yield, morphology, phase composition and magnetic properties of carbon-encapsulated iron nanoparticles was studied. The inclusion of Al surprisingly yielded an anomalous increase of austenite content. It was also found that the austenite content monotonically increases with the Al concentration in the anode. The inclusion of Al also diminished the structural ordering of carbon coatings and substantially narrowed the diameter distribution of encapsulated iron nanoparticles.

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