Effect of viscosity on harmonic signals from magnetic fluid

We explored the effect of viscosity on harmonic signals from a magnetic fluid. Using a numerical simulation that accounts for both the Brownian and Neel processes, we clarified how the magnetization mechanism is affected by viscosity. When the excitation field varies much slower than the Brownian relaxation Lime, magnetization can be described by the Langevin function. On the other hand, for the case when the excitation field varies much faster than the Brownian relaxation time, but much slower than the Neel relaxation time, the easy axes of the magnetic nanoparticles (MNPs) turn to some extent toward the direction of the excitation field in an equilibrium state. This alignment of the easy axes of MNPs caused by the AC field becomes more significant with the increase of the AC field strength. Consequently, the magnetization indifferent from the Langevin function even though Neel relaxation time is faster than time period of the external frequency, It is necessary to consider these results when we use harmonic signals from a magnetic fluid in a high-viscosity medium. (C) 2014 Elsevier B.V. All rights reserved,