Abstract
Vacuum evaporation method is a promising technique to prepare metallic magnetic fluids with high saturation magnetization. In the method, ferromagnetic metals or alloys are evaporated in vacuum and are deposited onto the surface of oil containing surfactant, then the products are subjected to a heat treatment to grow the particles up to the size desirable for magnetic fluids.
In this work, such the effects of the heating process on the Co magnetic fluids were investigated in further detail.
The particles of Co with diameter distributed arounds 2 nm before heating grew into the size of about 5 nm and were agglomerated after the heat treatment. The growth rate of particles increased with decrease of the concentration of the surfactant contained in the oil. From infrared spectra, the surfactant layer protectingthe particles were confirmed on the sample before heating. After heating, however, the infrared spectra characteristic for the surfactant layer became obscure ones. The agglomerated particles can be redispersed into a stable dispersion system by adding the surfactant. In this manner, Co magnetic fluids which has the highest saturation magnetic flux density of 680 G was obtained.
