Effect of viscosity on the AC magnetization of magnetic nanoparticles under different AC excitation fields

Yonetani, Takashi; Nakamura, Takuru; Higashi, Oji; Enpuku, Keiji

doi:10.1016/j.jmmm.2018.09.127

Cited by 17 publications

(12 citation statements)

References 26 publications

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“…The existence of the magnetic oscillation mode has also been confirmed in recent experiments 38 , 39 . Meanwhile, the results of SAR measurements of nanoparticle assemblies distributed in a liquid are usually compared 13 , 15 , 16 , 28 – 30 with the LRT predictions, although formally this theory can be valid only in a relatively weak magnetic field. In this work, using the previously developed approach 31 , detailed calculations of the SAR of a dilute assembly of iron oxide nanoparticles are performed depending on the particle diameters, the alternating magnetic field amplitude and the liquid viscosity.…”

Section: Introductionmentioning

confidence: 99%

Properties of assembly of superparamagnetic nanoparticles in viscous liquid

Usov

Rytov

Bautin

2021

Sci Rep

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Detailed calculations of the specific absorption rate (SAR) of a dilute assembly of iron oxide nanoparticles with effective uniaxial anisotropy dispersed in a liquid are performed depending on the particle diameters, the alternating (ac) magnetic field amplitude H0 and the liquid viscosity. For small and moderate H0 values with respect to particle anisotropy field Hk the SAR of the assembly as a function of the particle diameter passes through a characteristic maximum and then reaches a plateau, whereas for sufficiently large amplitudes, H0 ~ Hk, the SAR increases monotonically as a function of diameter. The realization of viscous and magnetic oscillation modes for particle unit magnetization vector and director for moderate and sufficiently large H0 values, respectively, explains this behavior. It is found that the SAR of the assembly changes inversely with the viscosity only in a viscous mode, for nanoparticles of sufficiently large diameters. In the magnetic mode the SAR of the assembly is practically independent of the viscosity, since in this case the nanoparticle director only weakly oscillates around the ac magnetic field direction. The conditions for the validity of the linear response theory have been clarified by comparison with the numerical simulation data.

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Section: Introductionmentioning

confidence: 99%

Properties of assembly of superparamagnetic nanoparticles in viscous liquid

Usov

Rytov

Bautin

2021

Sci Rep

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“…The existence of the magnetic oscillation mode has also been confirmed in recent experiments [38,39]. Meanwhile, the results of SAR measurements of nanoparticle assemblies distributed in a liquid are usually compared [13,15,16,[28][29][30] with the LRT predictions, although formally this theory can be valid only in a relatively weak magnetic field.…”

Section: Introductionmentioning

confidence: 83%

“…without invoking any additional hypotheses about the dynamic magnetic susceptibility of the assembly [27], or the relaxation times of nanoparticles [30,54]. Low-frequency hysteresis loops, examples of which are shown in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Although the assumption of the independence of relaxation processes is not obvious, the Shliomis hypothesis is widely used in the analysis of experimental results [13,16,[27][28][29][30]. In [26] the Shliomis relation was derived by an approximate solution of the Fokker -Planck equation in the limit of a weak external magnetic field.…”

Section: B Effective Relaxation Time Of Nanoparticle In Liquidmentioning

confidence: 99%

“…In subsequent works [25][26][27][28][29][30], various generalizations of LRT were developed, based on the introduction of the expressions for the dynamic magnetic susceptibility or for the relaxation times of superparamagnetic nanoparticles in a viscous liquid. An alternative approach was also developed [31][32][33][34][35][36] based on the use of a system of stochastic equations to describe the dynamics of the unit magnetization vector and the particle director at a finite temperature.…”

Section: Introductionmentioning

confidence: 99%

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Equilibrium properties of assembly of interacting superparamagnetic nanoparticles

Usov

Serebryakova

2020

Sci Rep

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Simultaneous temperature and viscosity estimation capability via magnetic nanoparticle relaxation

Ütkür

Sarıtaş

2022

Medical Physics

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Magnetic particle imaging (MPI) is emerging as a highly promising imaging modality. Magnetic nanoparticles (MNPs) are used as imaging tracers in MPI, and their relaxation behavior provides the foundation for its functional imaging capability. Since MNPs are also utilized in magnetic fluid hyperthermia (MFH) and MPI enables localized MFH, temperature mapping arises as an important application area of MPI.To achieve accurate temperature estimations, however, one must also take into account the confounding effects of viscosity on the MPI signal. In this work, we analyze the effects of temperature and viscosity on MNP relaxation and determine temperature and viscosity sensitivities of relaxation time constant estimations via TAURUS (TAU estimation via Recovery of Underlying mirror Symmetry) at a wide range of operating points to empower simultaneous mapping of these two parameters. Methods: A total of 15 samples were prepared to reach four target viscosity levels (0.9-3.6 mPa⋅s) at five different temperatures (25-45 • C). Experiments were performed on a magnetic particle spectrometer (MPS) setup at 60 different operating points at drive field amplitudes ranging between 5 and 25 mT and frequencies ranging between 1 and 7 kHz. To enable these extensive experiments, an in-house arbitrary-waveform MPS setup with temperature-controlled heating capability was developed. The operating points were divided into four groups with comparable signal levels to maximize signal gain during rapid signal acquisition. The relaxation time constants were estimated via TAURUS, by restoring the underlying mirror symmetry property of the positive and negative half cycles of the time-domain MNP response. The relative time constants with respect to the drive field period, τ, were computed to enable quantitative comparison across different operating points. At each operating point, a linear fit was performed to τ as a function of each functional parameter (i.e., temperature or viscosity). The slopes of these linear fits were utilized to compute the temperature and viscosity sensitivities of TAURUS. Results: Except for outlier behaviors at 1 kHz, the following global trends were observed: τ decreases with drive field amplitude, increases with drive field frequency, decreases with temperature, and increases with viscosity. The temperature sensitivity varies slowly across the operating points and reaches a maximum value of 1.18%/ • C. In contrast, viscosity sensitivity is high at low frequencies around 1 kHz with a maximum value of 13.4%/(mPa⋅s) but rapidly falls after 3 kHz. These results suggest that the simultaneous estimation of temperature and viscosity can be achieved by performing measurements at two different drive field settings that provide complementary temperature/viscosity sensitivities. Alternatively, temperature estimation alone can be achieved with a single measurement at drive field frequencies above 3 kHz, where viscosity sensitivity is minimized.

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Effect of viscosity on the AC magnetization of magnetic nanoparticles under different AC excitation fields

Cited by 17 publications

References 26 publications

Properties of assembly of superparamagnetic nanoparticles in viscous liquid

Properties of assembly of superparamagnetic nanoparticles in viscous liquid

Equilibrium properties of assembly of interacting superparamagnetic nanoparticles

Simultaneous temperature and viscosity estimation capability via magnetic nanoparticle relaxation

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