Magnetic fluid dynamics in a rotating magnetic field

The dynamics of a magnetic fluid in a rotating magnetic field in the presence of thermal noise were studied by performing numerical simulations based on the Fokker-Planck equation. We first clarified the dynamic properties by numerical simulation such as the frequency dependence of the fluid magnetization, the field-dependent relaxation time, and the M-H curve in a rotating magnetic field. Using the simulation results, we modified an existing analytical model and obtained an empirical expression to quantitatively describe the particle dynamics. The simulation results were compared with experimental results in a rotating magnetic field. The frequency dependence of the magnetization of the magnetic fluid was measured over the linear and nonlinear regions. In order to make a quantitative comparison, the hydrodynamic and effective core size distributions were independently estimated from measurements of the ac susceptibility and the M-H curve. The phase lag and amplitude in a rotating magnetic field obtained from our simulation agreed well with the experimental results. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3688254]