ABSTRACT
The liquid ferromagnetics, synthesised in the middle of the 60s of the 20th century – magnetic fluids (MF) – are colloidal solutions of various ferro-or ferrimagnetic substances in conventional fluids [34-40, 314]. The production of the magnetic fluids makes it possible to solve one of the most important tasks of colloidal chemistry – the production of nanoparticles of the solid material and dispersion of the material in the fluid-carrier [39-41]. As a result of these small dimensions of the particles, they become single-domain particles [34, 41]. In the absence of the magnetic field and in fields in which the para-process is not significant [41, 42], the single-domain particles can be regarded as magnetised to saturation. The magnetic moment of these particles is m* = VMS0, where V is the volume of the particles. Saturation magnetisation MS0 depends on the particle size and decreases with the reduction of the particle size; at the particle size typical of the magnetic colloids, MS0 is equal to ~50% of the appropriate value of the multi-domain material. The reduction of MS0 is attributed to the deficit of the neighbours in the volume interaction in the surface layer or to chemical changes in the surface layer of the particles [34, 35, 39].
