MAGNETIC-PROPERTIES OF NANOMETER-SCALE IRON PARTICLES GENERATED BY IRON ATOM CLUSTERING IN COLD PENTANE

Nanometer-scale iron particles have been prepared by iron atom clustering in cold pentane. Particle growth was terminated by adsorption of oleic acid, yielding air-stable particles ranging in size from 2 to 12 nm, that were amorphous according to XRD analysis. TEM analysis showed that the larger particles were prolate spheroids and the smaller ones were spherical. The original sample had a room-temperature saturation magnetization of Ms = 12.3 emu/g and a coercivity of Hc = 60 Oe. Following heat treatment with argon, the XRD results showed the following reaction scheme: oxidation to Fe3O4 at 360 °C and reduction to α-Fe at 520 °C (processes apparently due to adsorbed oleic acid). For the 520 °C treated sample, the room-temperature saturation magnetization and coercivity were Ms = 200 emu/g and Hc = 20 Oe, respectively. By pentane washing of the as-prepared sample, the smaller particles could be separated by filtration, leaving the larger 8–12-nm particles on the filter. This powdered sample trapped on the filter had Ms = 54.9 emu/g and Hc = 60 Oe. Heat treatment also caused oxidation to Fe3O4 at 360 °C and an incomplete reduction to α-Fe and FeO at 520 °C. For the 520 °C treated sample, the recorded room-temperature saturation magnetization and coercivity were Ms = 123.6 emu/g and Hc = 20 Oe, respectively. © 1990, American Chemical Society. All rights reserved.