Influence of ferrite stabilizing elements and Co on structure and magnetic properties of carbon-encapsulated iron nanoparticles synthesized in thermal plasma jet

Highlights: • Inclusion of ferrite stabilizing elements reduces the diameter of CEINs. • Inclusion of ferrite stabilizing elements increases the amount of austenite. • Inclusion of Al, Ti, Cr and V causes formation of few layer graphene. • Magnetic performance of CEINs can be largely improved by post annealing. - Abstract: The encapsulation of Fe nanoparticles in protective carbon coatings always leads to formation of undesired paramagnetic austenite phase. Various ferrite stabilizing elements were included in the synthesis process to verify whether their inclusion may minimize the austenite content in carbon-encapsulated iron nanoparticles synthesized in thermal plasma jet. Eight ferrite stabilizing elements (Si, Al, Mo, Ti, Zr, Cr, W and V) and one austenite promoting additive (Co) were tested. Their influence on the synthesis yield, phase composition, morphology and magnetic properties of carbon-encapsulated iron nanoparticles was studied. It was found that the addition of ferrite stabilizers strongly influences the diameter distribution, graphitization degree, phase composition and magnetic properties. Contrary to the thermodynamic predictions the inclusion of ferrite stabilizing elements caused a substantial worsening of magnetic performance in carbon-encapsulated iron nanoparticles. It has been also shown that the subsequent heat treatment of carbon-encapsulated iron nanoparticles significantly improves their magnetic properties