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Nanomaterials 2016, 6(9), 170; doi:10.3390/nano6090170

Rotation of Magnetization Derived from Brownian Relaxation in Magnetic Fluids of Different Viscosity Evaluated by Dynamic Hysteresis Measurements over a Wide Frequency Range

1
Department of Electrical and Electronic Engineering, Shizuoka University, Hamamatsu 432-8561, Japan
2
Department of Electrical and Computer Engineering, Yokohama National University, Yokohama 240-8501, Japan
*
Author to whom correspondence should be addressed.
Academic Editor: Thomas Nann
Received: 16 June 2016 / Revised: 1 September 2016 / Accepted: 5 September 2016 / Published: 10 September 2016
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Abstract

The dependence of magnetic relaxation on particle parameters, such as the size and anisotropy, has been conventionally discussed. In addition, the influences of external conditions, such as the intensity and frequency of the applied field, the surrounding viscosity, and the temperature on the magnetic relaxation have been researched. According to one of the basic theories regarding magnetic relaxation, the faster type of relaxation dominates the process. However, in this study, we reveal that Brownian and Néel relaxations coexist and that Brownian relaxation can occur after Néel relaxation despite having a longer relaxation time. To understand the mechanisms of Brownian rotation, alternating current (AC) hysteresis loops were measured in magnetic fluids of different viscosities. These loops conveyed the amplitude and phase delay of the magnetization. In addition, the intrinsic loss power (ILP) was calculated using the area of the AC hysteresis loops. The ILP also showed the magnetization response regarding the magnetic relaxation over a wide frequency range. To develop biomedical applications of magnetic nanoparticles, such as hyperthermia and magnetic particle imaging, it is necessary to understand the mechanisms of magnetic relaxation. View Full-Text
Keywords: magnetic nanoparticles; magnetic relaxation; hysteresis loop; magnetic fluid; viscosity magnetic nanoparticles; magnetic relaxation; hysteresis loop; magnetic fluid; viscosity
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MDPI and ACS Style

Ota, S.; Kitaguchi, R.; Takeda, R.; Yamada, T.; Takemura, Y. Rotation of Magnetization Derived from Brownian Relaxation in Magnetic Fluids of Different Viscosity Evaluated by Dynamic Hysteresis Measurements over a Wide Frequency Range. Nanomaterials 2016, 6, 170.

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