Preparation and Properties of Colloidal Ferromagnetic Metals

Preparation of Co and Fe ferromagnetic colloids using a mixture of oil-soluble surfactants and a saturated hydrocarbon oil is described. Amines with long-chain lipophilic alkyl radicals and sulfonates were used as the surfactants, and a drum was rotated to draw the liquid into a film while evaporating the metal in vacuum, gradually increasing the colloid concentration in the liquid. Monodisperse colloidal particles of uniform size (about 50 Å) were obtained. Co colloids formed in this way were super-paramagnetic at 246 K and above, and the colloidal particle concentration was 6 × 10¹⁶ to 2 × 10¹⁷. The temperature of transition to ferromagnetism varied with the surfactant used.