Editors : H.W. Hahn, D.L. Feldheim, C.P. Kubiak, R. Tannenbaum, R.W. Siegel
a1 Engineering Materials Physics Division, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
a2 Materials Chemistry Division, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
a3 XaarJet AB, SE-175 26 Järfälla, Sweden
We present a study on the magnetic behavior of nanosized iron oxide particles coated with different surfactants (sodium oleate, PVA and starch) in a ferrofluid. The effect of the coating material, and different particle concentrations in the ferrofluid have been magnetically investigated to determine the effective magnetic particle size and possible interaction. The superparamagnetic iron oxide particles, synthesized by a controlled co-precipitation technique, are found to contain magnetite (Fe3O4) as a main phase with a narrow physical particle size distribution between 6 and 8 nm. The mean effective magnetic size of the particles in different ferrofluid systems are estimated to be around 4-5 nm which is smaller than the physical particle size. On a 10% dilution in the starch coated ferrofluid we observe a decrease in the blocking temperature.