In this perspective article, we present a short selection of some of the most significant case studies on magnetic nanoparticles for potential applications in nanomedicine, mainly magnetic resonance. For almost 10 years, our research activity focused on the comprehension of the physical mechanisms on the basis of the nuclear relaxation of magnetic nanoparticles in the presence of magnetic fields; taking advantage of the insights gathered over this time span, we report on the dependence of the relaxation behaviour on the chemico-physical properties of magnetic nanoparticles and discuss them in full detail. In particular, a critical review is carried out on the correlations between their efficiency as contrast agents in magnetic resonance imaging and the magnetic core of magnetic nanoparticles (mainly iron oxides), their size and shape, and the coating and solvent used for making them biocompatible and well dispersible in physiological media. Finally, the heuristic model proposed by Roch and coworkers is presented, as it was extensively adopted to describe most of the experimental data sets. The large amount of data analyzed allowed us to highlight both the advantages and limitations of the model.

The effect of size, shape, coating and functionalization on nuclear relaxation properties in iron oxide core-shell nanoparticles: a brief review of the situation.

The magnetic properties of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ nanoparticle assemblies have been investigated in detail through a combination of vibrating sample magnetometry (VSM) and muon spin relaxation ($\ensuremath{\mu}\mathrm{S}\mathrm{R}$) techniques. Two samples with average particle sizes of 5 and 20 nm, respectively, were studied. For both samples, the VSM and $\ensuremath{\mu}\mathrm{S}\mathrm{R}$ results exhibit clear signatures of superparamagnetism at high temperature and magnetic blocking at low temperature. The $\ensuremath{\mu}\mathrm{S}\mathrm{R}$ data demonstrate that the transition from the superparamagnetic to the blocked state occurs gradually throughout the sample volume over an extended temperature range due to the finite particle size distribution of each nanoparticle batch. The transition occurs between approximately 3 and 45 K for the 5-nm nanoparticles and 150 and 300 K for the 20-nm nanoparticles. The VSM and $\ensuremath{\mu}\mathrm{S}\mathrm{R}$ data are further analyzed to yield estimates of microscopic magnetic parameters including the nanoparticle spin-flip activation energy ${E}_{A}$, magnetic anisotropy $K$, and intrinsic nanoparticle spin reversal attempt time ${\ensuremath{\tau}}_{0}$. These results highlight the complementary information about magnetic nanoparticles that can be obtained by bulk magnetic probes such as magnetometry and local magnetic probes such as $\ensuremath{\mu}\mathrm{S}\mathrm{R}$.

Superparamagnetic dynamics and blocking transition in Fe 3 O 4 nanoparticles probed by vibrating sample magnetometry and muon spin relaxation

The magnetic properties of Fe$_3$O$_4$ nanoparticle assemblies have been investigated in detail through a combination of vibrating sample magnetometry and muon spin relaxation ($\mu$SR) techniques. Two samples with average particle sizes of 5 nm and 20 nm, respectively, were studied. For both samples, the magnetometry and $\mu$SR results exhibit clear signatures of the superparmagnetic state at high temperature and the magnetically blocked state at low temperature. The $\mu$SR data demonstrate that the transition from the superparamagnetic to the blocked state occurs gradually throughout the sample volume over a broad temperature range due to the finite particle size distribution of each sample. The transition occurs between approximately 3 K and 45 K for the 5 nm sample and 150 K and 300 K for the 20 nm sample. The magnetometry and $\mu$SR data are further analyzed to yield estimates of microscopic magnetic parameters including the nanoparticle spin-flip activation energy $E_A$, magnetic anisotropy $K$, and intrinsic nanoparticle spin reversal attempt time $\tau_0$. These results highlight the complementary information about magnetic nanoparticles that can be obtained by bulk magnetic probes such as magnetometry and local magnetic probes such as $\mu$SR.

Superparamagnetic dynamics and blocking transition in Fe$_3$O$_4$ nanoparticles probed by vibrating sample magnetometry and muon spin relaxation

This thesis concerns the study of structural and magnetic properties of hollow magnetic nanoparticles (HMNPs), shell and shell/shell These HMNPs present enhanced surface effects resulting from the presence of both inner and outer surface layers The experimental investigation combining magne-tic measurements and 57Fe Mossbauer spectrometry of such HMNPs has revealed a complex spin magnetic structure Small HMNPs with ultrathin thickness show highly disordered magnetic structure and the corresponding in-field hyperfine structure can be described by means of 2 speromagnetic antiferromagnetically coupled, in addition to the significant exchange bias phenomenon The in-field Mossbauer study of the effect of size and thickness of HMNPs shows that the spin disorder is strongly correlated to the surface to volume ratio Those experimental magnetic behaviors were confirmed using Monte Carlo simulation Indeed, after improving the numeric model, it is concluded that surface anisotropy Ks has a dominant role in the magnetic behavior of HMNPs and the value of critical Ks necessary to obtain radial (spike) configuration decreases as the size of HMNPs increases, keeping the same thickness The numeric study for different sizes and shell thicknesses allows the effect of these parameters on the spin structure of HMNPs to be followed Then, the experi-mental study extended to shell/shell HMNPs indicates that the spin disorder is enhanced in HMNPs with antiferromagnetic shell (NiO) in addition to larger exchange bias field From those results, one can try to deduce the effect of spin disorder on the exchange bias phenomena in such system

/pdf/hollow-magnetic-nanoparticles-experimental-and-numerical-1gohnfad68.pdf

Hollow Magnetic Nanoparticles : experimental and numerical studies

Curvilinear Magnetic Shells

By means of muon spin relaxation measurements we unraveled the temperature spin dynamics in monodisperse maghemite spherical nanoparticles with different surface to volume ratio, in two samples wit ...

/pdf/low-temperature-anomalies-in-muon-spin-relaxation-of-solid-2i7uv17a5y.pdf

Low-temperature anomalies in muon spin relaxation of solid and hollow γ − F e 2 O 3 nanoparticles: A pathway to detect unusual local spin dynamics

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Low-temperature anomalies in muon spin relaxation of solid and hollow γ − F e 2 O 3 nanoparticles: A pathway to detect unusual local spin dynamics