We have synthesized maghemite (γ‐Fe 2 O 3 ) nanoparticles using chemical coprecipitation technique through a typical pipette drop method (pipette diameter: 2000 μm) and a piezoelectric nozzle method (nozzle size: 50 μm). 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 nm 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. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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Jeong et al. (2004) studied this question.