8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.76Wed 711:10-14:00Magnetostatic properties of dense ferrocolloidsAlexey Ivanov 1 and Ekaterina Elfimova 11 Urals State University, Lenin av. 51, 620000, Ekaterinburg, Russian FederationFerrocolloids (ferrofluids, magnetic fluids) are stable suspensions of nanoparticles of ferro- andferrimagnetic materials in liquid carriers. The characteristic diameter of the magnetic particles isabout 10 nm, and the particle shape is close to a sphere. Since the ferroparticle size is smaller thanthe single domain threshold, such particles are traditionally considered as uniformly magnetizedspheres. The ferrocolloids synthesized by now have record-breaking high values (∼ 100) of aninitial magnetic susceptibility at room temperatures. Such ferrocolloids are highly concentrated,and the intensity of interparticle dipole-dipole interaction exceeds the thermal energy. Any knowntheoretical model cannot describe so high values of the initial magnetic susceptibility. In presentwork the statistical model is developed for calculation of initial magnetic susceptibility of denseferrocolloids. The model is based on the relation between the initial magnetic susceptibility andthe pair correlation function of a system of dipolar spheres. Interactions between ferroparticles aremodeled by the sum of the steric interaction potential and the dipole-dipole potential. Two types ofsteric interaction are considered, these are the hard sphere repulsion and the square-well attraction.Using virial expansion of the pair correlation function we obtain expression for the initial magneticsusceptibility as a function of the ferroparticle volume concentration and the dipolar couplingconstant. The theory is being tested now against the experimental results and computer simulationdata. The work was supported by the Grant No. MK-1673. 2010. 2 of the President of RussianFederation.76