Influences of spinel type and polymeric surfactants on the size evolution of colloidal magnetic nanocrystals (MFe₂O₄, M= Fe, Mn)

Abstract

Two types of polymeric surfactants, PEG₃₀₀₀ and PVP₄₀₀₀₀, were used for the preparation of magnetic ferrite MFe₂O₄ (M = Mn, Fe) colloidal nanocrystals using a solvothermal reaction method. The effect of spinel type effect on the size evolution of various nanoparticles was investigated. It was found that Fe₃O₄ nanoparticles exhibited higher crystalinity and size evolution than MnFe₂O₄ nanoparticles with use of the two surfactants. It is proposed that this observation is due to fewer tendencies of surfactants on the surface of Fe₃O₄ building blocks nanoparticles than MnFe₂O₄. Less amounts of surfactant or capping agent on the surface of nanoparticles lead to the higher crystalibity and larger size. It is also suggested that the type of spinel (normal or inverted spinel) plays a key role on the affinity of the polymeric surfactant on the surface of building blocks.