Magnetic fluids

Natural liquid media exhibiting magnetic order are not known at present. The strongest magnetic properties are inherent in saturated molecular solutions of transition and rare-earth metals the magnetic susceptibility of which do no exceed the order of 10⁴. In virtue of this, specific effects detennined by the combination of magnetic properties with fluidity until recently have attracted little attention of research community. The situation changes markedly after artificial strongly magnetic liquids - colloidal solutions of ferromagnetic materials (about 10 nm in size) are synthesised in the middle of 60-ies. Small ferromagnetic particles consist of a single domain, consequently, the magnetic moment of an individual particle is about 10⁵ times larger than magnetic moments of transition or rare-earth metal ions. Therefore, eventual value of the Langevin paramagnetic susceptibility of a colloidal solution will exceed that of ions by the same order of magnitude, whereas saturation of magnetisation is reached at field values as low as about 1 kOe.