Theoretical Study of the Magnetization Dynamics of Nondilute Ferrofluids

The paper is devoted to the theoretical investigation of the magnetodipolar interparticle interaction effect on magnetization dynamics in moderately concentrated ferrofluids. We consider a homogenous (without particle aggregates) ferrofluid consisting of identical spherical particles and employ a rigid dipole model, where the magnetic moment of a particle is fixed with respect to the particle itself. In particular, for the magnetization relaxation after the external field is instantly switched off, we show that the magnetodipolar interaction leads to the increase of the initial magnetization relaxation time. For the complex ac susceptibility χ (ω) = χ′ (ω) +i χ″ (ω) we find that this interaction leads to an overall increase of χ″ (ω) and shifts the χ″ (ω) peak towards lower frequencies. Comparing results obtained with our analytical approach (second order virial expansion) to numerical simulation data (Langevin dynamics method), we demonstrate that the employed virial expansion approximation gives a good qualitative description of the ferrofluid magnetization dynamics and provides a satisfactory quantitative agreement with numerical simulations for the dc magnetization relaxation, up to the particle volume fraction ∼10%, and for the ac susceptibility, up to 5%. © 2009 The American Physical Society.This work has been done under the financial support of RFFI, Grants No. 06-01-00125, No. 07-02-00079, No. 07-01-960769Ural, No. 08-02-00647, Fund CRDF, No. PG07-005-02

Towards a theory of mechanical properties of ferrogels. Effect of chain-like aggregates

The paper deals with theoretical study of deformation of a ferrogel filled by magnetizable particles united in the chain-like aggregates. The sample is placed in a magnetic field parallel to the chains. Uniaxial elongation of the sample along the field is studied. Analysis shows that interaction of the particles in the chains and rupture of the chains by the elastic forces lead to non linear dependence of the macroscopical stress on the elongation strain. The theoretical results are in principle agreement with known experimental study of the ferrogels deformation. © 2016 Published by Elsevier B.V

Theoretical study of the magnetization dynamics of non-dilute ferrofluids

The paper is devoted to the theoretical investigation of the magnetodipolar interparticle interaction effect on remagnetization dynamics in moderately concentrated ferrofluids. We consider a homogeneous (without particle aggregates) ferrofluid consisting of identical spherical particles and employ a rigid dipole model, where magnetic moment of a particle is fixed with respect to the particle itself. In particular, for the magnetization relaxation after the external field is instantly switched off, we show that the magnetodipolar interaction leads to the increase of the initial magnetization relaxation time. For the complex ac-susceptibility we find that the this interaction leads to an overall increase of the imaginary susceptibility part and shifts the peak on its frequency dependence towards lower frequencies. Comparing results obtained with our analytical approach (second order virial expansion) to numerical simulation data (Langevin dynamics method), we demonstrate that the employed virial expansion approximation gives a good qualitative description of the ferrofluid magnetization dynamics and provides a satisfactory quantitative agreement with numerical simulations for the dc magnetization relaxation - up to the particle volume fraction c ~ 10% and for the ac-susceptibility - up to c ~ 5 %.Comment: 12 pages, 6 figures, submitted to PR

Kinetics of internal transformations in thermodynamically unstable ferrofluids

We present results of theoretical study of initial stage of spinodal decomposition and magneto-diffusion transport in ferrofluids with single-domain ferromagnetic nanoparticles. Effect of magnetic field and the long-ranged interparticle correlations on kinetics of this transformation is analyzed

To the theory of dynamical properties of non-dilute polydisperse ferrofluids

A theoretical model of dynamic susceptibility and magnetoviscous effect in non-dilute polydisperse ferrofluids with magnetically interacting particles is proposed. This system is considered as homogeneous magnetic colloid of interacting particles, without any heterogenous aggregates. Analysis is based on the mathematically regular approximation of the pair interparticle interaction combined with the effective field method, which leads to very good agreement with the laboratory and computer experiments in the case of dilute ferrofluids with non-interacting particles and with computer simulations of monodisperse ensembles of magnetically interacting ferromagnetic particles