Effect of surfactant concentration on the size of coated ferromagnetic nanoparticles

We demonstrate that the average size of the coated ferromagnetic Fe2O3 nano particles is controlled by the surfactant concentration in the coating solu tion. Magnetization as a function of this ratio first increases and then de creases exhibiting a peak. Surface area of the coated material shows invers e behavior, i.e. first decreases and then increases. Both curves have extre ma at the same ratio of surfactant/substrate. We explain these features in terms of competition between surface and volume contribution to the total e nergy, when surface contribution is determined by the bonding energy betwee n the surfactant SH-group and Fe2O3. We support our conclusions by employin g transmission electron microscopy and elemental analysis. (C) 1999 Elsevie r Science S.A. All rights reserved.