Size-effect induced cation redistribution on the magnetic properties of well-dispersed CoFe2O4 nanocrystals

This work reports the synthesis of size-controlled and well-dispersed CoFe2O4 nanocrystals through a facile thermal decomposition method, of which size can be simply tuned via the change of reaction time. The fcc Co or hcp Co impurities can be precipitated out in the CoFe2O4 nanocrystals by further prolonging the reaction time. Magnetic measurements show that the pure CoFe2O4 nanocrystals show sizedependent ferrimagnetism at room temperature, in which the saturation magnetization increases and the coercivity anomalously decreases as the particle size increases. The variation of magnetic properties is attributed to the surface-randomized spin and cations redistribution caused by surface effect and size effect. Besides, the precipitated Co impurities can greatly improve the saturation magnetization and coercivity of the CoFe2O4 nanocrystals. This paper provides a new path to tailor the magnetic properties of spinel ferrite nanostructures by tuning the cations distribution or adding magnetic impurities. (c) 2020 Elsevier B.V. All rights reserved.