On the influence of inertial effects, arising from rotational Brownian motion, on the complex susceptibility of ferrofluids

Fannin, P.C.; Charles, S.W.; Relihan, T

doi:10.1088/0022-3727/28/9/002

Cited by 13 publications

(7 citation statements)

References 6 publications

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“…Frequency dependent measured susceptibilities have been used to estimate the particle size distribution in ferrofluid 55 and infer typical effective relaxation times, s eff . 56,58 We fitted the Cole-Cole model 67 to the measured responses to estimate the characteristic effective time. (Figure 1(c)) was fitted with a log-normal distribution, with mean 27 nm and standard deviation 5.2 nm.…”

Section: B Nanoparticle Characterizationmentioning

confidence: 99%

“…A general treatment of the relaxation in ferrofluids based on a Fokker-Planck equation was given by Brown; 49 Rosensweig 40 used the effective relaxation time (1/s eff ¼ 1/s b þ 1/s n ) to calculate the power dissipation in a magnetic fluid under an AMF. The frequency dependence of relaxation of the MNP system can be determined experimentally by measuring the spectra of the complex susceptibility [50][51][52][53][54][55][56][57][58][59] or frequency dependent magnetic field responses from the MNPs.…”

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confidence: 99%

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Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

Shubitidze

Kekalo

Stigliano

et al. 2015

Journal of Applied Physics

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Magnetic nanoparticles (MNPs), referred to as the Dartmouth MNPs, which exhibit high specific absorption rate at low applied field strength have been developed for hyperthermia therapy applications. The MNPs consist of small (2-5 nm) single crystals of gamma-FeO with saccharide chains implanted in their crystalline structure, forming 20-40 nm flower-like aggregates with a hydrodynamic diameter of 110-120 nm. The MNPs form stable (>12 months) colloidal solutions in water and exhibit no hysteresis under an applied quasistatic magnetic field, and produce a significant amount of heat at field strengths as low as 100 Oe at 99-164 kHz. The MNP heating mechanisms under an alternating magnetic field (AMF) are discussed and analyzed quantitatively based on (a) the calculated multi-scale MNP interactions obtained using a three dimensional numerical model called the method of auxiliary sources, (b) measured MNP frequency spectra, and (c) quantified MNP friction losses based on magneto-viscous theory. The frequency responses and hysteresis curves of the Dartmouth MNPs are measured and compared to the modeled data. The specific absorption rate of the particles is measured at various AMF strengths and frequencies, and compared to commercially available MNPs. The comparisons demonstrate the superior heating properties of the Dartmouth MNPs at low field strengths (<250 Oe). This may extend MNP hyperthermia therapy to deeper tumors that were previously non-viable targets, potentially enabling the treatment of some of the most difficult cancers, such as pancreatic and rectal cancers, without damaging normal tissue.

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Section: B Nanoparticle Characterizationmentioning

confidence: 99%

mentioning

confidence: 99%

Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

Shubitidze

Kekalo

Stigliano

et al. 2015

Journal of Applied Physics

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“…An estimate of the balance can be made by considering the simple model of an isolated sphere descending through water under the influence of gravity. Considering a collection of magnetic particles in an aligned starting state the system magnetization, M , will decay exponentially as a function of time, t , according to the relationship M ( t ) = exp (− t /τ) (Debye 1929; Fannin et al 1995). For suspensions with constant viscosity τ is independent of concentration and is given by: where V is the particle volume, η is the fluid viscosity, k is Boltzmann's constant and T is the absolute temperature.…”

Section: Methodsmentioning

confidence: 99%

The role of magnetostatic interactions in sediment suspensions

Heslop¹,

Witt²,

Kleiner³

et al. 2006

Geophysical Journal International

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S U M M A R YThe processes that influence a detrital remanent magnetization as well as the physical microscale factors that control formation of a stable post-depositional remanent magnetization are still not fully understood. Previous laboratory studies and statistical numerical approaches have shown the possibility that sediment suspensions can display complex magnetization phenomena. Such behaviour has been attributed to the effect of magnetostatic interactions in the suspension, which could provide one explanation for spurious magnetizations observed in marine sediment cores. In laboratory experiments we investigated magnetization decay as a function of time in sediment suspensions produced with varying lithologies and particle concentrations. A companion model takes into account the physics of magnetic particleparticle interactions, Brownian motion and hydrodynamic forces to investigate numerically the magnetization behaviour of sediment suspensions. When combined, the experiments and the numerical models reveal a weak effect of magnetostatic interactions in the natural sediment suspensions, which is expressed as an increase in the magnetization decay rate. In addition, a calculation of effective particle size based on the response of each suspension to Brownian motion indicates that the majority of the sedimentary magnetic particles are attached to larger clay particles.

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“…Contrary to the case considered in Ref. [29], here the negative values of χ are due to the Larmor precession and not due to inertia effects since we consider a non-inertial model. Figure 4 shows the imaginary or loss part of the susceptibility as a function of frequency of the applied field.…”

Section: B Magnetic Susceptibilitymentioning

confidence: 91%

Diffusion-jump model for the combined Brownian and Néel relaxation dynamics of ferrofluids in the presence of external fields and flow

Ilg

2019

Phys. Rev. E

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ArticleAccepted Version Ilg, P. (2019) Diffusionjump model for the combined Brownian and Neel relaxation dynamics of ferrofluids in the presence of external fields and flow. Physical Review E, 100 (2). 022608.Relaxation of suspended magnetic nanoparticles occurs via Brownian rotational diffusion of the particle as well as internal magnetization dynamics. The latter is often modeled by the stochastic Landau-Lifshitz equation, but its numerical treatment becomes prohibitively expensive in many practical applications due to a time-scale separation between fast, Larmor-type precession and slow, barrier-crossing dynamics. Here, a diffusion-jump model is proposed to take advantage of the timescale separation and to approximate barrier-crossings as thermally activated jump processes that occur alongside rotational diffusion. The predictions of our diffusion-jump model are compared to reference results obtained by solving the stochastic Landau-Lifshitz equation coupled to rotational Brownian motion. Good agreement is found in the regime of high energy barriers where Néel relaxation can be considered a thermally activated rare event. While many works in the field have neglected Néel relaxation altogether, our approach opens the possibility to efficiently include Néel relaxation also into interacting many-particle models.

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On the influence of inertial effects, arising from rotational Brownian motion, on the complex susceptibility of ferrofluids

Cited by 13 publications

References 6 publications

Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

The role of magnetostatic interactions in sediment suspensions

Diffusion-jump model for the combined Brownian and Néel relaxation dynamics of ferrofluids in the presence of external fields and flow

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