SYNTHESIS, MICROSTRUCTURAL AND MAGNETIC CHARACTERIZATIONS OF SELF-ASSEMBLED HEMATITE NANOPARTICLES

Phase pure hematite nanoparticles coated with octyl ether and oleic acid were synthesized by a facile chemical route. Nanoparticles in the size range 7-25 nm were obtained by annealing the as-prepared samples at different temperatures. Transmission electron micrographs revealed that the particles tend to organize themselves in chain-like structures consisting of three to six nanoparticles along a common axis. The reason behind this oriented attachment is traced to the exchange coupling between the nanoparticles. Effect of exchange coupling was also evidenced as suppression of superparamagnetism in lower dimension hematite nanoparticles. Morin transition was observed around 260 K by magnetization measurement for hematite nanoparticles having average crystallite size of 25 nm.