Magnetic properties of iron nanoparticles in a polymer film

We systematically synthesized self-aggregated iron nanoparticles in the perfluorinated sulfo-cation membrane (MF-4SK) by ion-exchange method. Our experimental results show that iron nanoparticles in MF-4SK exhibit superparamagnetic properties above the blocking temperature. Field-cooled and zero-field-cooled magnetization data show the blocking temperature, T-B congruent to 120 K for the iron concentration of 5 x 10(19) atoms per 1 g of polymer film at 500 Oe applied field. This result is well matched with the calculation based on the temperature dependence of the coercivity, which shows T-B congruent to 110 K, with the zero temperature coercivity (H-C0) congruent to 420 Oe. The radius of the typical iron particle is deter-mined to be similar to 2 nm from transmission electron microscopy (TEM), showing good agreement with the value acquired by Langevin function fit. These experimental evidences suggest that iron nanoparticles in the polymer film obey a single-domain theory. (C) 2003 Elsevier Science B.V. All rights reserved.