Magnetic properties of γ-Fe2O3 nanoparticles made by coprecipitation method

We have synthesized maghemite (gamma-Fe2O3) nanoparticles using chemical coprecipitation technique through a typical pipette drop method (pipette diameter: 2000 mum) and a piezoelectric nozzle method (nozzle size: 50 pm). The size distribution of the maghemite nanoparticles prepared by the pipette drop method is from 5 nm to 8 nm. However, the nanoparticles made by the piezoelectric nozzle method show smaller size and very narrow size distribution from 3 nn to 5 nm. Zero-Field-Cooled (ZFC)/Field-Cooled (FC) magnetization and magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer from 5 K to 300 K to investigate the magnetic properties of nanoparticles. The SQUID measurements revealed superparamagnetism of nanoparticles with the blocking temperature of 119.5 K and 94.3 K for the nanoparticles made by the pipette drop method and the piezoelectric nozzle method, respectively. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.