Abstract

Magnetic nanoparticles with a narrow size distribution are desirable for applications in ultra-high density data storage and biomedicine. In this work, the size-selective precipitation and aggregate reduction were combined to classify superparamagnetic iron platinum- (FePt-) based nanoparticles. The size-selective precipitation was implemented with the variation in the amount of ethanol. In the first condition, the ratio of ethanol-to-nanosuspension of 3: 4 was used in the precipitation twice. By contrast, the second condition employed the ratios of ethanol-to-nanosuspension of 4: 4 in the first precipitation and 5: 4 in the second precipitation. The first precipitation successfully sorted out the aggregated particles, and the second precipitation collected particles with a narrow size distribution. The increase in ethanol enhanced the monodispersity of nanoparticles as shown by transmission electron microscopy (TEM) images and size distribution curves. In addition, large aggregated by-products from the precipitation stage were sonicated with the addition of surfactants. The increase in ultrasonic power reduces the aggregation, but the longer sonication led to an uneven distribution.