Effect of viscosity on harmonic signals from magnetic fluid
Effect of viscosity on harmonic signals from magnetic fluid
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DOI：
10.1016/j.jmmm.2014.10.044
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发表时间：
2015-04
影响因子：
2.7
通讯作者：
Takashi Yoshida;S. Bai;A. Hirokawa;K. Tanabe;K. Enpuku
中科院分区：
文献类型：
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作者：
Takashi Yoshida;S. Bai;A. Hirokawa;K. Tanabe;K. Enpuku
我们探讨了粘性对磁流体谐波信号的影响。通过对布朗过程和内尔过程的数值模拟，我们阐明了磁化机制如何受粘度的影响。当激发场的变化比布朗弛豫时间慢得多时，磁化强度可以用朗之万函数来描述。另一方面，对于当激发场变化比布朗弛豫时间快得多，但比Néel弛豫时间慢得多的情况，磁性纳米颗粒（MNP）的易磁化轴在一定程度上转向平衡状态下的激发场的方向。这种由交流电场引起的MNP易磁化轴的排列随着交流电场强度的增加而变得更加显著。因此，即使Néel弛豫时间比外部频率的时间周期快，磁化强度也不同于朗之万函数。当我们使用高粘度介质中磁流体的谐波信号时，有必要考虑这些结果。
We explored the effect of viscosity on harmonic signals from a magnetic fluid. Using a numerical simulation that accounts for both the Brownian and Néel processes, we clarified how the magnetization mechanism is affected by viscosity. When the excitation field varies much slower than the Brownian relaxation time, 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 Néel 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 is different from the Langevin function even though Néel 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.