Rotational dynamics of magnetic particles in suspensions

Abstract

An approach for the rotational dynamics of magnetic particles and their magnetic moments, in fluid suspensions, is developed. A possible application is to magnetic resonance in ferrofluids. Based on a generalized Lagrangian formulation for the equations of motion of the particle, we introduce its interaction with the solvent fluid via dissipative and random noise torques, as well as the interaction between the particle and its magnetic moment, treated as an independent physical entity and characterized by three generalized coordinates: its two polar angles and its modulus. In the appropriate limits, it reduces to the cases of superparamagnetic particles or nonsuperparamagnetic ͑blocked magnetic moments͒ particles. It is also indicated how the dynamic complex susceptibility may be calculated from the equations of motion, and as an example the effect of the particles inertia on the susceptibility is numerically evaluated for some arbitrary values of the parameters.

Improved efficiency of heat generation in nonlinear dynamics of magnetic nanoparticles

“…Nonlinear dynamics of the magnetization in single-domain ferromagnetic nanoparticle systems has received considerable attention due to a wide range of their applicability such as magnetic resonance imaging, ultrahigh density magnetic data recording, spintronics, and ferrofluids and in biomedical engineering, in particular, drug delivery or hyperthermia [1][2][3]. Among many forms of hyperthermia, the local induction of heat via magnetic nanoparticles seems a fruitful strategy with promising preclinical results in different cancer modes [4].…”

Ferrofluids: properties and applications

“…Bellow T B the particle is not anymore superparamagnetic, but the magnetic fluid is still superparamagnetic because the particle, and so also µ, continues to be quasi-free to rotate. Equations of motion for µ, sufficiently general to be applicable for the cases of superparamagnetic and non-superparamagnetic particles, as well as mixed situations, where both mechanisms are important, can be found in the literature [22,23]. Some hypothesis which are usually made in theoretical proposals for the rotational dynamics of the superparamagnetic particles and their magnetic moments in ferrofluids are:…”

Computer simulation of the stochastic dynamics of super-paramagnetic particles in ferrofluids

“…2) The particle's magnetic moment µ has constant modulus µ and can rotate inside the particle under the influence of an interaction potential modeled by V = −K(µ · c) 2 , where K is a constant, called "anisotropy constant"; we will use units such that µ = 1;…”

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Several papers have been written on the complex problem of the stochastic dynamics of the magnetic moments of super-paramagnetic particles, simultaneously with the stochastic rotation of these colloidal particles in a ferrofluid [1][2][3]. None of these works, however, is sufficiently general and conveniently simple and clear to be used in sumulational works to appropriately describe the experimental super-paramagntetic resonance lines.

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