Simultaneous Study of Brownian and Néel Relaxation Phenomena in Ferrofluids by Mössbauer Spectroscopy

Landers, Joachim; Salamon, Soma; Remmer, Hilke; Ludwig, Frank; Wende, Heiko

doi:10.1021/acs.nanolett.5b04409

Cited by 40 publications

(33 citation statements)

References 28 publications

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“…4(c) . The peak in χ ” is attributed to either Brownian rotation of the nanoparticle or Néel relaxation of nanoparticle moment and occurs at a frequency that is given by the inverse of the nanoparticle moment relaxation time 37 – 39 . The magnetic fluctuation spectra are proportional to χ ” through the fluctuation-dissipation theorem.…”

Section: Resultsmentioning

confidence: 99%

“…For in vivo biomedical applications, magnetic nanoparticles may be lodged in highly viscous tissues that reduce the Brownian rotation. The particle rotation needs to overcome the surface friction in a viscous fluid, which happens at a rotational frequency 38 , 39 where, k B is Boltzmann’s constant, T is the temperature, η is the viscosity of the fluid and R H is the hydrodynamic radius of the nanoparticle. In the case of Néel relaxation the magnetic moment needs to overcome the anisotropy energy barrier and the fluctuation rate is given by where K a is the anisotropy energy density, V is the particle volume, and f 0 is the attempt frequency, here chosen to be 1 GHz.…”

Section: Methodsmentioning

confidence: 99%

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Large T1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

Yin

Russek

Zabow

et al. 2018

Sci Rep

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Superparamagnetic iron oxide nanoparticles (SPIONs) are widely investigated and utilized as magnetic resonance imaging (MRI) contrast and therapy agents due to their large magnetic moments. Local field inhomogeneities caused by these high magnetic moments are used to generate T2 contrast in clinical high-field MRI, resulting in signal loss (darker contrast). Here we present strong T1 contrast enhancement (brighter contrast) from SPIONs (diameters from 11 nm to 22 nm) as observed in the ultra-low field (ULF) MRI at 0.13 mT. We have achieved a high longitudinal relaxivity for 18 nm SPION solutions, r1 = 615 s−1 mM−1, which is two orders of magnitude larger than typical commercial Gd-based T1 contrast agents operating at high fields (1.5 T and 3 T). The significantly enhanced r1 value at ultra-low fields is attributed to the coupling of proton spins with SPION magnetic fluctuations (Brownian and Néel) associated with a low frequency peak in the imaginary part of AC susceptibility (χ”). SPION-based T1-weighted ULF MRI has the advantages of enhanced signal, shorter imaging times, and iron-oxide-based nontoxic biocompatible agents. This approach shows promise to become a functional imaging technique, similar to PET, where low spatial resolution is compensated for by important functional information.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Large T1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

Yin

Russek

Zabow

et al. 2018

Sci Rep

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“…For the untreated dust sample, T B is around 60 K, while a heating temperature of 600 K already raises T B to approximately 125 K. The trend of increasing blocking temperatures continues with every tempering event until no more magnetite can be detected in the chondritic powder at approximately 1250 K. This indicates a growth of nanophase Fe 3 O 4 as well as possibly an agglomeration of multiple individual adjacent crystals. Using isolated magnetite nanoparticles as a reference, the increase of T B suggests a growth beginning at approximately 4 − 5 nm to 15 − 20 nm for powders heated up to 800 K (Landers et al (2016); Goya et al (2003); Häggström et al (2008)). As particle size in general, but also the size of asperities on surfaces, is important for sticking forces, this influences the effective surface energy.…”

Section: Influence Of Tempering On Nm-grain Sizesmentioning

confidence: 99%

Drifting inwards in protoplanetary discs I Sticking of chondritic dust at increasing temperatures

Bogdan

Pillich

Landers

et al. 2020

A&A

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Sticking properties rule the early phases of pebble growth in protoplanetary discs in which grains regularly travel from cold, water-rich regions to the warm inner part. This drift affects composition, grain size, morphology, and water content as grains experience ever higher temperatures. In this study we tempered chondritic dust under vacuum up to 1400 K. Afterwards, we measured the splitting tensile strength of millimetre-sized dust aggregates. The deduced effective surface energy starts out as γe = 0.07 J m−2. This value is dominated by abundant iron-oxides as measured by Mössbauer spectroscopy. Up to 1250 K, γe continuously decreases by up to a factor five. Olivines dominate at higher temperature. Beyond 1300 K dust grains significantly grow in size. The γe no longer decreases but the large grain size restricts the capability of growing aggregates. Beyond 1400 K aggregation is no longer possible. Overall, under the conditions probed, the stability of dust pebbles would decrease towards the star. In view of a minimum aggregate size required to trigger drag instabilities it becomes increasingly harder to seed planetesimal formation closer to a star.

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“…The line broadening in ferrofluids may also arise from the Néel relaxation [20][21][22]. In the studied case, Fe 2 O 3 particles are antiferromagnetic or weakly ferromagnetic.…”

Section: Resultsmentioning

confidence: 93%

Frictionless mobility of submicron particles in model viscid fluid

2019

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The mechanism of inter-and intracellular diffusional transport by vesicles in living organisms is poorly understood at the molecular scale. The diffusion of submicron and nanoparticles in dense media has been treated by numerous theoretical models. We face this problem experimentally using Mössbauer spectroscopy. On a characteristic for this method narrow time scale (≈10 −7 s), the velocity distribution of 120 nm spherical Fe 2 O 3 particles suspended in a 60% water solution of sucrose was determined by analyzing the 57 Fe Mössbauer spectral line profile. The particles usually exhibit classical Brownian motion, but their main diffusion mechanism is related to infrequent ( f≈10 6 s −1 ) but distant (d≈1 nm) translations. During such movements, the particles experience a minimal friction described by the temporal local viscosity, η loc ≈28 μPa·s.

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Simultaneous Study of Brownian and Néel Relaxation Phenomena in Ferrofluids by Mössbauer Spectroscopy

Cited by 40 publications

References 28 publications

Large T1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

Large T1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

Drifting inwards in protoplanetary discs I Sticking of chondritic dust at increasing temperatures

Frictionless mobility of submicron particles in model viscid fluid

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