  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.
