Magnetophoresis of ferrofluid in microchannel system and its nonlinear   effect
  We have studied the magnetophoretic particle separation and its nonlinear behavior of ferrofluids in microchannel which is proposed by Furlani. The magnetic gradient force is caused by an bias field and the polarized magnets and is found to be spatially uniform in the channel section which can be used for particle selecting or separation. We have derived the equations of nonlinear magnetization of magnetic particles which cause the harmonics of magnetophoresis. The Langevin model and generalized Clausius-Mossotti equation used show how the normal and longitude anomalous anisotropic effect the permeability of ferrofluids, thus the magnetic force. Our analysis demonstrates the viability of using the microchannel system for various bioapplications and other characterization of fluid transporting and the time-varying magnetic field can be potentially used for an integrated magnetometer and influences the the viscosity and effective permeability in ferrofluids. 
Y. C. Jian (1,2), L. F. Zhang (1) and J. P. Huang (1) ((1)Surface   Physics Laboratory (National Key Laboratory) and Departm...