Controlling the size of magnetic nanoparticles using pluronic block copolymer surfactants.

We have successfully controlled the size of magnetic nanoparticles by adjusting the surfactant/solvent ratio. Gamma-Fe(2)O(3) nanoparticles of 5.6 and 12.7, and Fe(0) nanoparticles of 22.3 nm in diameter were prepared, all having spherical shape and uniform size as confirmed by TEM. Mössbauer spectra confirmed Fe(3+) for the 5.6 and 12.7 nm particles and Fe(3+) and Fe(0) 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 Fe(0). T-M measurements show superparamagnetism for 5.6 and 12.7 nm particles and ferromagnetism for 22.3 nm particles.