Effective particle magnetic moment of multi-core particles

Ahrentorp, Fredrik; Astalan, Andrea Prieto; Blomgren, Jakob; Jonasson, Christian; Wetterskog, Erik; Svedlindh, Peter; Lak, Aidin; Ludwig, Frank; IJzendoorn, Leo van Lj; Westphal, Fritz; Grüttner, Cordula; Gehrke, Nicole; Gustafsson, Stefan; Olsson, Eva; Johansson, Christer

doi:10.1016/j.jmmm.2014.09.070

Cited by 41 publications

(45 citation statements)

References 15 publications

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“…The quite good agreement between agg DCM f and TB f could indicate that most of the agglomerated particles are thermally blocked, due to dipolar interactions. As shown in [60], a blocking of the macrospins in agglomerates of normally superparamagnetic particles can result in increased effective moments of the agglomerates, compared to the individual particles. This could also explain the observed peak in the high moment range (10 10 Am…”

Section: Numerical Inversionmentioning

confidence: 98%

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Distribution functions of magnetic nanoparticles determined by a numerical inversion method

et al. 2017

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In the present study, we applied a regularized inversion method to extract the particle size, magnetic moment and relaxation-time distribution of magnetic nanoparticles from small-angle x-ray scattering (SAXS), DC magnetization (DCM) and AC susceptibility (ACS) measurements. For the measurements the particles were colloidally dispersed in water. At first approximation the particles could be assumed to be spherically shaped and homogeneously magnetized single-domain particles. As model functions for the inversion, we used the particle form factor of a sphere (SAXS), the Langevin function (DCM) and the Debye model (ACS). The extracted distributions exhibited features/peaks that could be distinctly attributed to the individually dispersed and non-interacting nanoparticles. Further analysis of these peaks enabled, in combination with a prior characterization of the particle ensemble by electron microscopy and dynamic light scattering, a detailed structural and magnetic characterization of the particles. Additionally, all three extracted distributions featured peaks, which indicated deviations of the scattering (SAXS), magnetization (DCM) or relaxation (ACS) behavior from the one expected for individually dispersed, homogeneously magnetized nanoparticles. These deviations could be mainly attributed to partial agglomeration (SAXS, DCM, ACS), uncorrelated surface spins (DCM) and/or intra-well relaxation processes (ACS). The main advantage of the numerical inversion method is that no ad hoc assumptions regarding the line shape of the extracted distribution functions are required, which enabled the detection of these contributions. We highlighted this by comparing the results with the results obtained by standard model fits, where the functional form of the distributions was a priori assumed to be log-normal shaped.

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Section: Numerical Inversionmentioning

confidence: 98%

“…The other peaks describe magnetization contributions that lead to deviations from the simple Langevin-type behavior, e.g. the uncorrelated surface spins or agglomerates [59,60].…”

Section: Numerical Inversionmentioning

confidence: 99%

Distribution functions of magnetic nanoparticles determined by a numerical inversion method

et al. 2017

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“…5b. Both Brownian and Néel relaxation mechanisms can be assumed if the particles as a whole and their inside magnetic moments are free to rotate in the frequency scan [44]. The real part of the susceptibility at the low frequency limit slightly decreased (~10%) and the characteristic frequency of Néel relaxation shifted from 1300 to ~450 Hz as a result of coating the MNPs with the comb-like copolymer.…”

Section: Magnetic Properties Of the Naked And Core-shell Mnpsmentioning

confidence: 99%

Multifunctional PEG-carboxylate copolymer coated superparamagnetic iron oxide nanoparticles for biomedical application

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et al. 2018

Journal of Magnetism and Magnetic Materials

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Highlights• Multicore magnetite nanoparticles (MNPs) were superparamagnetic.• PEG-carboxylate polyelectrolytes coat spontaneously MNPs and stabilize them electrosterically.• Biofunction can be attached to MNPs via carboxylated coating layer.• Multifunctional shell prevents MNPs' internalization into cells.• Superparamagnetic property is sustained after MNP coating. AbstractBiocompatible magnetite nanoparticles (MNPs) were prepared by post-coating the magnetic nanocores with a synthetic polymer designed specifically to shield the particles from nonspecific interaction with cells. Poly(ethylene glycol) methyl ether methacrylate (PEGMA) macromonomers and acrylic acid (AA) small molecular monomers were chemically coupled by quasi-living atom transfer radical polymerization (ATRP) to a comb-like copolymer, P(PEGMA-co-AA) designated here as P(PEGMA-AA). The polymer contains pendant carboxylate moieties near the backbone and PEG side chains. It is able to bind spontaneously to MNPs; stabilize the particles electrostatically via the carboxylate moieties and sterically via the PEG moieties; provide high protein repellency via the structured PEG layer; and anchor bioactive proteins via peptide bond formation with the free carboxylate groups. The presence of the P(PEGMA-AA) coating was verified in XPS experiments. The electrosteric (i.e., combined electrostatic and steric) stabilization is efficient down to pH 4 (at 10 mM ionic strength). Static magnetization and AC susceptibility measurements showed that the P(PEGMA-AA)@MNPs are superparamagnetic with a saturation magnetization value of 55 emu/g and that both single core nanoparticles and multicore structures are present in the samples. The multicore components make our product well suited for magnetic hyperthermia applications (SAR values up to 17.44 W/g). In vitro biocompatibility, cell internalization, and magnetic hyperthermia studies demonstrate the excellent theranostic potential of our product. Graphical abstract

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“…A special class of 3D ensembles of magnetic nanoparticles are particle core aggregates or clusters, also referred to as multi-core nanoparticles [37]. Investigation of such particles has attracted much interest in recent years [38][39][40][41], mainly motivated by their large potential for biomedical applications [42,43].…”

Section: Introductionmentioning

confidence: 99%

Dipolar-coupled moment correlations in clusters of magnetic nanoparticles

et al. 2018

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Here, we resolve the nature of the moment coupling between 10-nm DMSA-coated magnetic nanoparticles. The individual iron oxide cores were composed of > 95 % maghemite and agglomerated to clusters. At room temperature the ensemble behaved as a superparamagnet according to Mössbauer and magnetization measurements, however, with clear signs of dipolar interactions. Analysis of temperature-dependent AC susceptibility data in the superparamagnetic regime indicates a tendency for dipolar coupled anticorrelations of the core moments within the clusters. To resolve the directional correlations between the particle moments we performed polarized small-angle neutron scattering and determined the magnetic spin-flip cross-section of the powder in low magnetic field at 300 K. We extract the underlying magnetic correlation function of the magnetization vector field by an indirect Fourier transform of the cross-section. The correlation function suggests non-stochastic preferential alignment between neighboring moments despite thermal fluctuations, with anticorrelations clearly dominating for next-nearest moments. These tendencies are confirmed by Monte Carlo simulations of such core-clusters.

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Effective particle magnetic moment of multi-core particles

Cited by 41 publications

References 15 publications

Distribution functions of magnetic nanoparticles determined by a numerical inversion method

Distribution functions of magnetic nanoparticles determined by a numerical inversion method

Multifunctional PEG-carboxylate copolymer coated superparamagnetic iron oxide nanoparticles for biomedical application

Dipolar-coupled moment correlations in clusters of magnetic nanoparticles

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