Nonlinear behavior of magnetic fluid in brownian relaxation: Numerical simulation and derivation of empirical model

Abstract

Nonlinear Brownian relaxation of magnetic fluids for the case of large excitation field was studied in relation to its biomedical applications. The Fokker-Planck equation, which describes the nonlinear behavior of magnetic fluids, was solved by numerical simulation when ac field was applied. Frequency-dependences of the harmonics were investigated in terms of the effective Brownian relaxation time τeff, which was empirically obtained from the ac susceptibility of the fundamental component. It was shown that higher harmonics become small even at ωτeff=1 compared to each quasi-static harmonics amplitudes.