Magnetic Field Dependence of Ni Nanorod Brownian Relaxation

Remmer, Hilke; Gratz, Micha; Tschöpe, Andreas; Ludwig, Frank

doi:10.1109/tmag.2017.2701145

Cited by 14 publications

(7 citation statements)

References 10 publications

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“…They were fitted with the phenomenological Havriliak−Negami model 24 for a precise determination of the characteristic peak positions. As expected and known from previous studies, 25,26 the characteristic Brownian peak shifts to higher frequencies and its amplitude decreases with increasing field amplitude. The characteristic frequency positions are plotted in Figure 3b…”

Section: ■ Results and Discussionsupporting

confidence: 91%

“…In ref , Yoshida and Enpuku numerically solved the Fokker–Planck equation for Brownian MNPs exposed to a large sinusoidal magnetic field and derived the following empirical equation for the Brownian relaxation time Here, ξ = mB /( k B T ) is the Langevin parameter with the particle magnetic moment m and the applied flux density B . As we demonstrated in refs and , this empirical equation is a good approximation to determine the magnetic moment and the zero-field Brownian relaxation time from the field dependence of ACS spectra.…”

Section: Resultsmentioning

confidence: 67%

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In-Field Orientation and Dynamics of Ferrofluids Studied by Mössbauer Spectroscopy

Landers

Salamon

Remmer

et al. 2018

ACS Appl. Mater. Interfaces

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By studying the response behavior of ferrofluids of 6–22 nm maghemite nanoparticles in glycerol solution exposed to external magnetic fields, we demonstrate the ability of Mössbauer spectroscopy to access a variety of particle dynamics and static magnetic particle characteristics at the same time, offering an extensive characterization of ferrofluids for in-field applications; field-dependent particle alignment and particle mobility in terms of Brownian motion have been extracted simultaneously from a series of Mössbauer spectra for single-core particles as well as for particle agglomerates. Additionally, information on Néel superspin relaxation and surface spin frustration could be directly inferred from this analysis. Parameters regarding Brownian particle dynamics, as well as Néel-type relaxation behavior, obtained via Mössbauer spectroscopy, have been verified by complementary AC-susceptometry experiments, modulating the AC-field amplitude, and using an extended frequency range of 10–1 to 106 Hz, while field-dependent particle alignment has been cross-checked via magnetometry.

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Section: ■ Results and Discussionsupporting

confidence: 91%

Section: Resultsmentioning

confidence: 67%

In-Field Orientation and Dynamics of Ferrofluids Studied by Mössbauer Spectroscopy

Landers

Salamon

Remmer

et al. 2018

ACS Appl. Mater. Interfaces

Self Cite

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“…For the ACS approximation, the deviation is mainly visible for the highest β 0values and it is found to be below 4% relative to the maximum amplitude for β 0 < 30, and below 5% for β 0 < 100. The approximation developed by Yoshida and Enpuku 2 was shown to describe the peak position of χ 1 for β 0 -values up to 100 15 ; however, their approximation showed a maximum deviation of the curves from the Fokker-Planck results that was about 10% for β 0 = 10, and up to 50% for β 0 = 100. If this approximation is used to fit the entire curve rather than only the peak position, such large deviations between the approximation and exact simulations can produce significant errors in the fitting result.…”

Section: Low-field Behaviourmentioning

confidence: 92%

“…Yoshida and Enpuku developed an analytical approximation to the magnetic susceptibility by fitting phenomenological expressions to the increase in the peak position of the imaginary part of the magnetic susceptibility and the ratio between the real and imaginary part at low frequency 14 . A slightly improved expression introduced by Ludwig et al 2 was shown to fit the peak position of the imaginary part of the magnetic susceptibility for large applied magnetic field amplitudes 15 . Later Gratz and Tschöpe also proposed an improved ACS approximation by fitting the Debye model to spectra obtained from Fokker-Planck calculations 16 .…”

Section: Introductionmentioning

confidence: 99%

Field-dependent dynamic responses from dilute magnetic nanoparticle dispersions

et al. 2018

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The response of magnetic nanoparticles (MNPs) to an oscillating magnetic field outside the linear response region is important for several applications including magnetic hyperthermia, magnetic resonance imaging and biodetection. The size and magnetic moment are two critical parameters for the performance of a colloidal MNP dispersion. We present and demonstrate the use of optomagnetic (OM) and AC susceptibility (ACS) measurements vs. frequency and magnetic field strength to obtain the size and magnetic moment distributions including the correlation between the distributions. The correlation between the size and the magnetic moment contains information on the morphology and intrinsic structure of the particle. In OM measurements, the variation of the second harmonic light transmission through a dispersion of MNPs is measured in response to an oscillating magnetic field. We solve the Fokker-Planck equations for MNPs with a permanent magnetic moment, and develop analytical approximations to the ACS and the OM signals that also account for the change in the curve shapes with increasing field strength. Further, we describe the influence of induced magnetic moments on the signals, by solving the Fokker-Planck equation for particles, which apart from the permanent magnetic moment may also have an induced magnetic moment and shape anisotropy. Using the results from the Fokker-Planck calculations we fit ACS and OM measurements on two multi-core particle systems. The obtained fit parameters also describe the correlations between the magnetic moment and size of the particles. From such an analysis on a commercially available polydisperse multicore particle system with an average particle size of 80 nm, we find that the MNP magnetic moment is proportional to the square root of the hydrodynamic size.

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“…At 25 mT a rough increase of approximately a factor four to about 72 kHz is to be expected. The plot was realized utilizing an approximation (Equation (4)) from Yoshida et al [24] based on solving the Fokker-Planck equation, which was experimentally verified [25,26]: 1.72 (4) can be seen in Equation (6).…”

Section: Magnetismmentioning

confidence: 96%

Biophysical Characterization of (Silica-coated) Cobalt Ferrite Nanoparticles for Hyperthermia Treatment

et al. 2019

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Magnetic hyperthermia is a technique that describes the heating of material through an external magnetic field. Classic hyperthermia is a medical condition where the human body overheats, being usually triggered by a heat stroke, which can lead to severe damage to organs and tissue due to the denaturation of cells. In modern medicine, hyperthermia can be deliberately induced to specified parts of the body to destroy malignant cells. Magnetic hyperthermia describes the way that this overheating is induced and it has the inherent advantage of being a minimal invasive method when compared to traditional surgery methods. This work presents a particle system that offers huge potential for hyperthermia treatments, given its good loss value, i.e., the particles dissipate a lot of heat to their surroundings when treated with an ac magnetic field. The measurements were performed in a low-cost custom hyperthermia setup. Additional toxicity assessments on Jurkat cells show a very low short-term toxicity on the particles and a moderate low toxicity after two days due to the prevalent health concerns towards nanoparticles in organisms.

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Magnetic Field Dependence of Ni Nanorod Brownian Relaxation

Cited by 14 publications

References 10 publications

In-Field Orientation and Dynamics of Ferrofluids Studied by Mössbauer Spectroscopy

In-Field Orientation and Dynamics of Ferrofluids Studied by Mössbauer Spectroscopy

Field-dependent dynamic responses from dilute magnetic nanoparticle dispersions

Biophysical Characterization of (Silica-coated) Cobalt Ferrite Nanoparticles for Hyperthermia Treatment

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