Synthesis of magnetically exchange coupled CoFe2O4/CoFe2 core/shell composite particles through spray pyrolysis

Magnetically exchange coupled CoFe2O4/CoFe2 composite particles were synthesized through spray pyrolysis, followed by H2 reduction. The H2 concentration was controlled to be 5, 8 and 10 vol%, respectively, in three parallel experiments. The products show a core/shell structure, with CoFe2O4 as the core, and CoFe2 as the shell. The structure is confirmed by TEM-EDX and STEM analysis. The XRD patterns indicate the existence of both CoFe2O4 and CoFe2 phases in the composites. The magnetic hysteresis loop of CoFe2O4/CoFe2 composite particles reduced by 5 vol% H2 is smooth and kink-free, indicating an effective exchange coupling between CoFe2O4 and CoFe2. Henkel Plots are further used to investigate the magnetic exchange coupling in the composites. This paper presented a convenient, environmentally friendly and effective method to synthetize magnetically exchange coupled composite particles.