Effect of laser radiation on magnetite nanoparticles in deposited ferrofluid

The processes in a system of nanoparticles of a concentrated colloidal solution of magnetite induced by laser light with a wavelength of 650 $\mu$m have been studied. It was found that radiation focused on a drying drop of this substance, under certain conditions, leads to the formation of large accumulations of particles, in some cases strongly protruding above the surface of the sediment or, on the contrary, to their displacement from the illuminated area. A qualitative discussion of possible mechanisms of the observed phenomena is carried out.