New Syntheses of Cobalt Ferrite Particles in the Range 2−5 nm:  Comparison of the Magnetic Properties of the Nanosized Particles in Dispersed Fluid or in Powder Form

Abstract

The size of cobalt ferrite particles from 2 to 5 nm is controlled by the reactant concentration in oil-in-water micelles. It is possible to obtain the particles either suspended in the solvent to form ferrofluid or in dry powder. When particles are isolated in a fluid, the interactions between particles are small. The magnetic size is similar to that determined by TEM. The reduced susceptibility increases progressively with the size of the particles and does not reach a plateau. With dry powder made of nanosized particles, the magnetic size is higher than that observed by TEM. Likewise, the reduced susceptibility strongly increases with increasing the particle size to reach a plateau for an average size equal to 3 nm. These are explained by the increase in the attractive interactions between particles. By heating the powder, the reduced remanence, M r /M s , and the coercivity, H c , increase with the increase in annealing temperature. This is attributed to the increase in the particle size and to the release of the adsorbed surfactant on the particles. The largest size of particles can be obtained either by annealing of the smallest one or from direct synthesis at room temperature. For a given size, the improvement in coercivity with annealing temperature is attributed to a better-defined nanocrystalline structure and to the release of surfactant to the particle interface.

Size-Selective Chemical Synthesis of Tartrate Stabilized Cobalt Ferrite Ionic Magnetic Fluid

“…The diameter D Mag of the magnetic core is smaller than the physical diameter of the particles D TEM . Similar results have already been reported (22). There are two reasons for that: the layer of fluctuating disordered spins present at the surface of the magnetically ordered core inside the nanocrystal and the layer of tartrate species adsorbed.…”

Dependence of magnetic properties on crystallite size of CoFe2O4nanoparticles synthesised by auto-combustion method

“…Various methods, including co-precipitation [7,8], hydrothermal synthesis [9,10], sol-gel techniques [11], microemulsion method [12,13], forced hydrolysis method [14] and sonochemical reaction [15], have been reported for preparing CoFe 2 O 4 . Most of these methods suffer with troublesome post-treatment and cannot be applied to a large-scale and economic production.…”

Nanoparticles of : Synthesis and superparamagnetic properties

“…However the crystallinity of the material is poor and the amount of material is highly reduced. In our laboratory we recently developed a new technique by using functionalized surfactant which forms oil in water micelles [18][19][20][21][22]. This technique needs a rather low reactant concentration (the reactant is the counter ion of the surfactant) and the chemical reaction takes place at room temperature.…”