Rotational dynamics of magnetic particles in suspensions - art. no. 011504

An approach for the rotational dynamics of magnetic particles and their mag netic moments, in fluid suspensions, is developed. A possible application i s to magnetic resonance in ferrofluids. Based on a generalized Lagrangian f ormulation for the equations of motion of the particle, we introduce its in teraction with the solvent fluid via dissipative and random noise torques, as well as the interaction between the particle and its magnetic moment, tr eated as an independent physical entity and characterized by three generali zed coordinates: its two polar angles and its modulus. In the appropriate l imits, it reduces to the cases of superparamagnetic particles or nonsuperpa ramagnetic (blocked magnetic moments) particles. It is also indicated how t he dynamic complex susceptibility may be calculated from the equations of m otion, and as an example the effect of the particles inertia on the suscept ibility is numerically evaluated for some arbitrary values of the parameter s.