Fluids with magnetic characteristics have important values for today applications. This fluids, so called
ferrofluids or magnetic fluids are in general formed by small nanoparticles with mean diameters about 10 nm
and a carrier liquid. In our work we present nanopowders obtained by laser pyrolysis, which have
characteristics for magnetic fluids applications. The important feature of powder was determined by means of
XRD and electron microscopy techniques. The nanopowders have sizes distributed in interval from 2 nm to
10 nm. The high resolution images exhibits single particles with magnetic monodomain. Also, we investigate
nanoparticles for defects. The nanoparticles forms nanoclusters, and high resolution image show adjacent
particles without interface, the coupling mode is only magnetic not chemical. The powders are composed by
magnetite and maghemite phase determined from XRD data, and confirmed by SAED and HRTEM work. The cell parameter calculated from the (220), (311), (511) (440) peaks of sample SF32 is 0.835 nm equal to
the maghemite cell parameter.
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