Magnetic properties of nanoscale iron particles

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Abstract
Nanoscale 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 while the smaller ones were spherical. The as-prepared sample had a room-temperature saturation magnetization of Ms=12.3 emu/g and a coercivity of Hc=60 Oe. Following heat treatment under 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 of this sample 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.