Size-dependent magnetic properties of γ-Fe₂O₃ nanocrystallites

A route for synthesizing monodisperse magnetic nanocrystallites of maghemite, [Formula: see text]-Fe₂O₃, with various sizes has been revisited. A systematic investigation of three [Formula: see text]-Fe₂O₃ nanocrystalline samples by different techniques has been performed to characterize their size-dependent magnetic properties. Zero-field-cooled and field-cooled magnetization measurements reveal that the superparamagnetic blocking temperatures are around 230 K, 170 K, and 50 K for the 15.0 nm, 11.8 nm, and 6.1 nm nanocrystallites, respectively. Low-temperature Mössbauer spectra show that all three nanocrystallites have the maghemite structure with all the vacancies in the B-sites. Furthermore, detailed analysis shows that there are more vacancies on the B-sites for the 6.1 nm nanocrystallites compared to 0.33 for the bulk maghemite.