Controlling the Size of Magnetic Nanoparticles Using Pluronic Block Copolymer Surfactants

Abstract

We have successfully controlled the size of magnetic nanoparticles by adjusting the surfactant/solvent ratio. γ-Fe₂O₃ nanoparticles of 5.6 and 12.7, and Fe⁰ nanoparticles of 22.3 nm in diameter were prepared, all having spherical shape and uniform size as confirmed by TEM. Mössbauer spectra confirmed Fe³⁺ for the 5.6 and 12.7 nm particles and Fe³⁺ and Fe⁰ for 22.3 nm particles, in good agreement with synchrotron XRD patterns. Both room temperature and 5 K H−M measurements show that 22.3 nm particles have much higher magnetization than their oxide counterparts, in agreement with their being Fe⁰. T−M measurements show superparamagnetism for 5.6 and 12.7 nm particles and ferromagnetism for 22.3 nm particles.