Magnetic Properties of gamma-Fe_2O_3 Nanoparticles Prepared by Laser Ablation

摘要

A new method of preparing nanoparticles by pulsed-laser ablation of a tiny wire was reported, and pure maghemite (gamma-Fe_2O_3) nanoparticles were synthesized by this method in a mixed gas flux of N_2 and O_2 at atmospheric pressure. The obtained gamma-Fe_2O_3 nanoparliles were in the range of 5 to 80 nm in diameter and largely spherical in shape. Structural characteristics and morphologies of the nanoparticles were characterized by XRD and TEM, respectively. Moreover, magnetic properties of the obtained gamma-Fe_2O_3 nanopartiles in the temperature range of 300 to 773 K were investigated. The experimental results demonstrate that the squareness value of the hysteresis loop decreases with increasing temperature. Both the coercivity and the saturation magnetization of the gamma-Fe_2O_3 nanoparticles show a constantly decreasing trend with increasing temperature up to the occurrence of the transformation from gamma-Fe_2O_3 to alpha-Fe_2O_3. Especially, at the temperature of 773 K, the gamma-Fe_2O_3 begins to transform to the alpha-Fe_2O_3 phase and the hysteresis loop becomes unclosed.