Characterization and magnetic properties of nanoparticles based on FePt solid solution with an oxide shell

• We investigated particles that have core–shell structure, where core material is a solid solution FexPt1−x and shell consists of γ-Fe2O3 with spinel structure.
• It is defined that exchange bias field increases with the increase of oxide shell thickness.
• Coercive force after annealing decreases due to decrease of ferromagnetic particles concentration.
• Analysis of exchange bias field and coercive force measurements for FePt systems of different effective thicknesses of components showed the possibility to control magnetic hardness of the studied system.

We present the results of magnetic properties investigations of ferromagnetic nanoparticles which ensembled with ferromagnetic shell. The aim of this work is to study the connection of structure–phase composition and thermal treatment with the magnetic properties, partially, with the coercive force and the exchange bias field in a two-dimension spin system of core–shell type. It is found that the exchange bias field increases with the growth of the oxide shell thickness. This is realized by annealing in a dosed oxygen flow. The decrease of the coercive force with the increase of annealing temperature is connected with the concentration effect (the concentration of ferromagnetic particles decreases).