Magnetic properties of dense ferrofluids: An influence of interparticle correlations

Abstract

A statistical model has been developed describing the magnetostatic properties of dense ferrocolloids and the dielectric properties of polar fluids. The model is based on the relation between the magnetization and the pair correlation function of a spatially homogeneous system of dipole particles. This approach allows us to calculate the ferrofluid magnetization (polarization density of polar fluid) in a form of expansion over both the particle concentration and the potential of the interparticle dipole-dipole interaction U(d). The obtained expressions for the ferrocolloid initial magnetic susceptibility, the dielectric constant of polar fluid and the ferrofluid magnetization with the accuracy approximately U(2)(d) describe well the experimental data and the results of computer modeling. The model justifies the validity of the "modified mean-field approach," and the effective field is calculated as a function of the Langevin magnetization.

Magnetic Properties of Colloidal Suspensions of Interacting Magnetic Particles

“…The proposed theories were mostly extensions of those already used to describe χ. For example, the one by Ivanov and Kuznetsova [124] compares well with experimental data. However, recent numerical simulations by Wang et al [126,128] for χ and M(H) are not well described by this theory when the volume fraction of the magnetic particles is small and the dipolar coupling is strong: they are better explained by a model of small non-interacting chains of different…”

“…Thus, when this equation is expanded in φλ one does not recover the general O(φ 2 λ 2 )-term of (4.12) while it is reproduced in the expression for the initial susceptibility. The authors also demonstrate that M and χ are not functions of the product φλ alone as predicted in [124] and that the theory [124] Raşa et al [130] measure in 2002 the initial susceptibility and the magnetization of ferrofluids at various stages of dilution. The susceptibility is found to be best described by…”

“…The second theory has also been applied to explain experimental data for a highly concentrated ferrofluid, as has a related cluster expansion result by Ivanov and Kuznetsova [124].…”

“…(4.11). When comparing the results of [124] with those of the cluster expansion [64] one has to be aware that in [124] some calculated terms that do not contribute to the initial susceptibility were discarded in order to be able to write the result in the form (4.13). Thus, when this equation is expanded in φλ one does not recover the general O(φ 2 λ 2 )-term of (4.12) while it is reproduced in the expression for the initial susceptibility.…”

Measuring the deformation of a ferrogel sphere in a homogeneous magnetic field

“…The solid line displays an approximation with the model presented in Ref. [24]. The sample is superparamagnetic with an initial susceptibility χ 0 = 0.81.…”