Fe-Co Alloy Nanoparticles Dispersed in Polymer-Derived Carbon Support: Effect of Initial Polymer Nature on the Size, Structure and Magnetic Properties

Fe-Co alloy nanoparticles with different sizes, supported by carbon derived from several polymers, namely polyacrylonitrile, polyvinyl alcohol and chitosan, have been synthesized by a one-pot method involving simultaneous metal nanoparticle formation and polymer carbonization. The method involves the joint dissolution of metal salts and a polymer, followed by annealing of the resulting dried film. Detailed XRD analysis confirmed the formation of Fe-Co alloy nanoparticles in each sample, regardless of the initial polymer used. Transmission electron microscopy images showed that the Fe-Co nanoparticles were all spherical, were homogeneously distributed within the carbon support and varied by size depending on the initial polymer nature and synthesis temperature. Fe-Co nanoparticles supported by polyacrylonitrile-derived carbon exhibited the smallest size (6-12 nm), whereas nanoparticles on chitosan-derived carbon support were characterized by the largest particle size (13-38 nm). The size dependence of magnetic properties were studied by a vibrating sample magnetometer at room temperature. For the first time, the critical particle size of Fe-Co alloy nanoparticles with equiatomic composition has been experimentally determined as 13 nm, indicating the transition of magnetic properties from ferromagnetic to superparamagnetic.

Automated summary

Fe-Co alloy nanoparticles with different sizes have been successfully synthesized using a one-pot method, and their morphology and distribution have been characterized by XRD and TEM. The results show that the size of the nanoparticles is influenced by the nature of the initial polymer and synthesis temperature, and the critical particle size of equiatomic Fe-Co alloy nanoparticles has been determined.