Exchange-spring effect in CoFe2O4/CoFe2 composite nano-particles

CoFe2O4/CoFe2 composite nano-particles were synthesized by heating CoFe2O4 nano-particles in reducing atmosphere at 300 degrees C and 400 degrees C. Their composition, microstructure and magnetic properties were investigated. It was found that the product of reducing CoFe2O4 at 300 degrees C iscomposed by CoFe2O4 nano-particles and a small amount of CoFe2 nano-alloy. Based on the negative values of Henkel plots and the two-phase behavior in magnetic hysteresis loop the dominant inter-particle dipole coupling was confirmed. But in the process of reducing CoFe2O4 at 400 degrees C, surface layers of CoFe2 were formed on the CoFe2O4 nano-particles, and exchange coupling appeared at the interface of both phases, which was confirmed from the positive values of Henkel plots. (C) 2013 Elsevier B. V. All rights reserved.