Magnetic Moments Of Nanoparticles Research Articles

Interparticle magnetic interactions and magnetic field dependence of superparamagnetic blocking temperature in ferrihydrite nanoparticle powder systems

In this study, nanoparticles of initial synthetic ferrihydrite have been coated with arabinogalactan. The synthesized series of samples with different degrees of coverage of particles has been characterized by X-ray photoelectron spectroscopy, Mössbauer spectroscopy, transmission electron microscopy and magnetometry. The superparamagnetic blocking temperature decreases monotonically with an increase in the degree of coverage of ferrihydrite particles, which is unambiguously related to the different role of the interparticle magnetic interactions in the investigated powder systems. Analysis of the field dependence of the blocking temperature within the random anisotropy model has shown that an increase in the degree of coverage of ferrihydrite particles leads to a decrease in the size of a cluster in which the behaviors of the nanoparticle magnetic moments are correlated. The results obtained have shown the possibility of effective control of the strength of magnetic interparticle interactions in powder ferrihydrite systems by coating nanoparticles with arabinogalactan.

Spin dynamics in ensembles of ultrafine ferrihydrite nanoparticles

Features of the spin dynamics in ensembles of interacting (FH-chem) and weakly interacting (FH-coated) magnetic ultrasmall ($\ensuremath{\langle}d\ensuremath{\rangle}\ensuremath{\sim}2$ nm) ferrihydrite nanoparticles have been explored. The dc and ac magnetic susceptibilities $[{\ensuremath{\chi}}^{\ensuremath{'}}(T)$ and ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}(T)]$ of the investigated samples have been thoroughly measured in a weak magnetic field (2 Oe) around the temperatures of superparamagnetic blocking of the nanoparticle magnetic moments (19 and 50.4 K for FH-coated and FH-chem, respectively, according to the dc magnetization data). It has been shown that the magnetic interactions between nanoparticles induce the formation of the cluster spin-glass state below the superparamagnetic blocking temperature (${T}_{g}=18$ and 49.5 K for FH-coated and FH-chem, respectively). It has been found that coating of nanoparticles increases the critical scaling index from $z\ensuremath{\nu}=5.9$ (FH-chem) to $z\ensuremath{\nu}=8.0$ (FH-coated). This indicates a general slowdown of the dynamics of correlated spins, which is also expressed as an increase in relaxation time ${\ensuremath{\tau}}_{0}$ after switching on the interparticle interactions. We attribute this phenomenon to a consequence of a change in the volume of correlated spins with the increasing size of a cluster of interacting nanoparticles. It has been demonstrated using the simulated ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}(T)$ dependence that the dissipation of the magnetic energy occurs in two independent stages. The first stage is directly related to the blocking of the nanoparticle magnetic moments, while the second stage reflects the spin-glass behavior of surface spins and depends strongly on the intensity of the interparticle interactions.

Role of Magnetic Nanoparticles Size and Concentration on Structural Changes and Corresponding Magneto-Optical Behavior of Nematic Liquid Crystals.

The effect of magnetic nanoparticles size and concentration on nematic liquid crystal (NLC) behavior in a magnetic field was investigated. The magneto-optical investigation using measurements of the light transmission through the liquid crystal was used to study the structural changes induced by an applied weak magnetic field. Magnetic nanoparticles Fe3O4 of spherical shape with different size and volume concentration were added to NLC 4-cyano-40 -hexylbiphenyl (6CB) during its isotropic phase. In contrast to undoped liquid crystals, the distinctive different light transmission responses induced by a magnetic field in studied NLC samples were observed suggesting both structural changes and the orientational coupling between magnetic moments of nanoparticles and the director of the NLC. Experimental measurements were conducted, including investigation under linearly increasing and/or jumped magnetic field, respectively, as well as the investigation of time influence on structural changes to study their stability and switching time. The analysis of observed light transmission characteristics confirmed the role of concentration and size of magnetic nanoparticles on the resultant behavior of investigated NLC compounds. The obtained results showed the lowering of the threshold magnetic field with an increase in the volume concentration of nanoparticles and on the important role of nanoparticles size on stability and switching properties. Obtained results are discussed within the context of previous ones.

Magnetic properties of textured ferrocomposite consisting of immobilized superparamagnetic nanoparticles.

Wide use of magnetic nanoparticles in modern technologies and biomedical applications requires reliable theoretical models capable of predicting physical properties. Solidification of a ferroparticle suspension under the action of permanent magnetic field allows us to obtain a ferrocomposite, characterized by some orientational texture of the nanoparticle easy magnetization axes. The static magnetic response of this ferrocomposite differs from that of the parent magnetic suspension due to "freezing" of nanoparticle translational and rotational degrees of freedom. Here the superparamagnetic fluctuations of the nanoparticle magnetic moments play a key role in the formation of the ferrocomposite magnetic response depending on the degree of orientational ordering, obtained during synthesis of a ferrocomposite. With the help of statistical mechanics we calculate the magnetization and the initial magnetic susceptibility of the textured ferrocomposite for various temperatures and magnetic field strengths. The easy axis texturing leads to a significant increase of the magnetic properties, and the effect intensifies with the growth of nanoparticle magnetocrystalline anisotropy. Theoretical predictions are supported by Monte Carlo simulations. The obtained results evidence that the texturing of a ferroparticle suspension and transforming it into a textured ferrocomposite are a real way to enhance the magnetic response of these magnetic soft materials.

Viscoelastic and dielectric properties of 5CB nematic liquid crystal doped by magnetic and nonmagnetic nanoparticles.

In this article we show how spherical nanoparticles (NPs) imposing planar anchoring can strongly impact the viscoelastic, dielectric, and electro-optical properties of a nematic liquid crystal when they are not aggregated. We also demonstrate that when the NPs are magnetic, most nematic properties are more impacted than when they are nonmagnetic. With magnetic NPs a molecular disorder is induced that decreases the nematic order parameter, this decrease impacting the values of elastic constants, viscosity, and response time. The impact on 5CB liquid crystal (LC) has been investigated with spherical nanoparticles (NPs) of identical size around 6 nm, magnetic (γFe_{2}O_{3}), and nonmagnetic (CeO_{2}) ones that are both surface functionalized by poly(aminopropylmethylsiloxane-b-dimethylsiloxane) (PAPMS-b-PDMS) block copolymer ligands to promote planar anchoring. In the presence of nonmagnetic NPs, despite an almost constant nematic order parameter, a significant decrease of elastic constants (25.4%), viscosity (22%), and response time (23%) is measured. It suggests a dilution effect for the intermolecular interactions in the presence of NPs. This hypothesis is supported by the observation of an enhanced decrease of the same nematic parameters in the presence of magnetic NPs that can be fully explained by the corresponding order parameter decrease. This finally leads to a remarkable decrease of the splay elastic constant by 51% in the presence of magnetic NPs. The decrease of the nematic order parameter by 18% in the presence of magnetic NPs demonstrates that the NP magnetic moments are only weakly coupled to the nematic director and consequently only induce a disorder in the composite system. A significant influence of the expected large LC structural modifications in the presence of magnetic NPs is, however, shown by a particularly large increase of the diffusion coefficient 43% and large decrease of the dielectric anisotropy (43%). We believe that the observed impact of NPs with planar anchoring on nematic properties could be extended to most spherical NPs if their aggregation can be avoided. In particular, the difference between magnetic and nonmagnetic NPs could be extended to ferroelectric and nonferroelectric NPs.

The effect of permanent magnetic field on photoluminescence of nanopowder oxides produced by pulsed electron beam evaporation

The effect of a permanent magnetic field on shift of photoluminescent peaks of nanopowder oxides produced by pulsed electron beam evaporation in vacuum has been discovered for the first time. It has been established that when the magnetic field of 0.154 T is superimposed, shifts in photoluminescence spectrum maxima are observed for Al2O3 in the yellow region (14 nm) and for CeO2 in the red region (50 nm). It is possible that the shifts are a consequence of the interaction of the permanent magnetic field with the magnetic moments of nanoparticles that are defective in nature.

Investigation of structural changes in oil-based magnetic fluids by surface acoustic waves

Surface acoustic waves (SAWs) are used for the first time to investigate structural changes in transformer oil-based magnetic fluids under magnetic field. The measurement of the attenuation of SAW propagating along the interface between magnetic fluid and the piezoelectric substrate is showed as an effective tool to study such processes in the case of magnetic fluids when the obviously utilized longitudinal acoustic waves due to the higher viscosity are not available. The magnetic particles FeO.Fe2O3 in several different volume concentrations, from 0.05% to 3.5%, were added to the transformer oil MOL. Both linear increasing and jumped changed magnetic field were applied to study structural changes. The interaction between the magnetic field and magnetic moments of nanoparticles can lead to the aggregation of magnetic nanoparticles and following chain or cluster formations that have an influence on the SAW attenuation. The concentration of magnetic nanoparticles and temperature of magnetic fluid have a decisive influence on structural changes due to the changes of viscosity and thermal motion with the increasing temperature that both affect the process of cluster formation. The measurement of the acoustic anisotropy and applying the theoretical predictions gives additional useful information about the structure of nanoparticles formations in investigated magnetic fluids. Obtained results are compared and discussed.

Magnetic behavior of superparamagnetic nanoparticles containing chelated transition metal ions

Abstract Superparamagnetic nanoparticles functionalized with diethylenetriaminepentaacetic acid (MagNP@DTPA) have been employed for extracting and processing strategic metal ions in nanohydrometallurgy. In order to probe the metal ion capture from aqueous solution in real time, an external weighing device has been adapted for a conventional analytical balance, allowing to measure the nanoparticles attraction by a miniature neodymium (Nd2Fe14B) supermagnet. The magnetic migration kinetics, also referred as magnetophoresis, has been probed in this way, as well as the evaluation of the magnetic interaction of the Fe3O4 core with the attached paramagnetic metal ions. The results indicated some correlation between the overall nanoparticle magnetic moments and their magnetophoretic rates. An additive magnetic response was observed for the metallated nanoparticles in dry form, using VSM. However, in solution, the global magnetization decreased with the magnetic moment of the attached metal ions. Presumably, there is an influence of dipolar and superexchange interactions mediated by the metal-ligand structures, including the formation of carboxylate bridges between the outer paramagnetic centers in the dry form.

The accelerated removal of kidney stones by concomitant use of camel thorn distillate and Rowatinex drug: A case report

The coupled magnetic and mechanical motion of a ferromagnetic nanoparticle in a viscous fluid is considered within the dynamical approach. The equation based on the total momentum conservation law is used for the description of the mechanical rotation, while the modified Landau-Lifshitz-Gilbert equation is utilized for the description of the internal magnetic dynamics. The exact expressions for the particles trajectories and the power loss are obtained in the linear approximation. The comparison with the results of other widespread approaches, such as the model of fixed particle and the model of rigid dipole, is performed. It is established that in the small oscillations mode the damping precession of the nanoparticle magnetic moment is the main channel of energy dissipation, but the motion of the nanoparticle easy axis can significantly influence the value of the resulting power loss.

Light-assisted spontaneous birefringence and magnetic-domain formation in a suspension of gyrotropic nanoparticles

We show that linearly polarized light in a suspension of gyrotropic nanoparticles can experience modulation instability, which leads to spatial separation of right- and left-circularly polarized waves. Such a separation preserves zero full angular momentum of the electromagnetic field; thus, the time-reversal symmetry is broken only locally. Eventually, this instability results in the formation of the lattice of spatial solitons with alternating right and left circular polarization. As magnetic moments of nanoparticles tend to reorient parallel to the wave vector in circularly polarized light, every spatial soliton captures a static magnetic field directed along or opposite to the wave vector depending on the direction of the field angular momentum; therefore, the soliton lattice altogether looks like an array of magnetic domains with antiferromagnetic ordering.

Quantitative Analysis of Magnetic Nanoparticles by Means of Magnetic Force Microscopy

Magnetic force microscopy (MFM) is a powerful and simple tool to analyze magnetic materials and structures down to the nano-meter scale. However, there is still a demand for satisfactory models describing measured MFM data quantitatively, thereby allowing us to quantitatively analyze the magnetic properties of the sample. Here, we present an application of the recently proposed pseudo-pole model, which assumes that the tip can be represented by a cone covered homogeneously with dipoles pointing to the tip of the cone. Nano-composites of ferromagnetic Co nanoparticles (NPs) made by inert gas condensation and subsequently deposited non-magnetic SiO x cover layers with different layer thicknesses on single-crystalline Si substrates have been investigated in this paper. We extract quantitative information about the magnetization of individual NPs, as well as their depth below the surface of the SiO x films. In addition, we present an alternative method to extract information about the NP magnetic moment from the width of the NP signal in lift images, which does not require knowledge about the van der Waals interaction. We find good agreement between the magnetic moments determined by both approaches.

Pinning of domain walls in two-layer ferromagnetic nanowire with scattering fields of nanoparticles

The results of a micromagnetic simulation of the pinning-depinning processes of a domain wall (DW) in a rectangular ferromagnetic nanowire (NW) consisting of two magnetic layers with scattering fields of two rectangular two-layer nanoparticles (NPs) located on NW opposite sides and oriented perpendicular to its axis are presented. The features of magnetization reversal of this system in the external magnetic field are studied depending on direction of the magnetic moments of the nanoparticle layers. The value of the depinning field in such a system depends essentially on mutual orientation of NP magnetic moments and NW magnetization. The possibility to realize a magnetic logic cell performing the “conjunction” operation of ternary logic is discussed.

Manifestation of strong magneto-electric dipolar coupling in ferromagnetic nanoparticles−FLC composite: evaluation of time-dependent memory effect

ABSTRACTRod-shaped 5 wt.% copper-doped ZnO (ZnO:Cu2+) ferromagnetic nanoparticles (NPs), prepared by hydrothermal method, were dispersed in ferroelectric liquid crystal (FLC) named Felix 17/100. The effect of ferromagnetic NPs on the physical properties of FLC material (Felix 17/100) has been investigated by dielectric, electro-optical and polarising optical microscopic methods. A noteworthy time-dependent memory has been observed in the NPs-dispersed FLC composite attributed to the coupling of magnetic field associated to NPs with the director orientation of FLC. Improvement in spontaneous polarisation and dielectric susceptibility of FLC material has been ensued with the addition of ferromagnetic NPs. Faster electro-optic response, at lower applied voltage, has also been observed in NPs-dispersed FLC composite. These changes are accredited to the magneto-electric dipolar coupling existing due to the interactions between magnetic-dipole and electric-dipole moments of magnetic NPs and FLC material, respectively. The formation of periodic domains capable to show memory effect has been observed in composite. The observed time-dependent memory was confirmed by dielectric and electro-optical methods. FLC material enriched with the properties of ferromagnetic NPs can be utilised in advanced multifunctional optical devices, time-dependent memory-based security devices and computational purposes.

Power loss for a periodically driven ferromagnetic nanoparticle in a viscous fluid: The finite anisotropy aspects

The coupled magnetic and mechanical motion of a ferromagnetic nanoparticle in a viscous fluid is considered within the dynamical approach. The equation based on the total momentum conservation law is used for the description of the mechanical rotation, while the modified Landau-Lifshitz-Gilbert equation is utilized for the description of the internal magnetic dynamics. The exact expressions for the particles trajectories and the power loss are obtained in the linear approximation. The comparison with the results of other widespread approaches, such as the model of fixed particle and the model of rigid dipole, is performed. It is established that in the small oscillations mode the damping precession of the nanoparticle magnetic moment is the main channel of energy dissipation, but the motion of the nanoparticle easy axis can significantly influence the value of the resulting power loss.

Interaction Effects in Assembly of Magnetic Nanoparticles

A specific absorption rate of a dilute assembly of various random clusters of iron oxide nanoparticles in alternating magnetic field has been calculated using Landau–Lifshitz stochastic equation. This approach simultaneously takes into account both the presence of thermal fluctuations of the nanoparticle magnetic moments and magneto-dipole interaction between the nanoparticles of the clusters. It is shown that for usual 3D clusters, the intensity of the magneto-dipole interaction is determined mainly by the cluster packing density η = NpV/Vcl, where Np is the average number of the particles in the cluster, V is the nanoparticle volume, and Vcl is the cluster volume. The area of the low frequency hysteresis loop and the assembly-specific absorption rate have been found to be considerably reduced when the packing density of the clusters increases in the range of 0.005 ≤ η < 0.4. The dependence of the specific absorption rate on the mean nanoparticle diameter is retained with an increase of η, but becomes less pronounced. For fractal clusters of nanoparticles, which arise in biological media, in addition to a considerable reduction of the absorption rate, the absorption maximum is shifted to smaller particle diameters. It is found also that the specific absorption rate of fractal clusters increases appreciably with an increase of the thickness of nonmagnetic shells at the nanoparticle surfaces.

Integrated microHall magnetometer to measure the magnetic properties of nanoparticles.

Magnetic nanoparticles (MNPs) are widely used in biomedical and clinical applications, including medical imaging, therapeutics, and biological sample processing. Rapid characterization of MNPs, notably their magnetic moments, should facilitate optimization of particle synthesis and accelerate assay development. Here, we report a compact and low-cost magnetometer for fast, on-site MNP characterization. Termed integrated microHall magnetometer (iHM), our device was fabricated using standard semiconductor processes: an array of Hall sensors, transistor switches, and amplifiers were integrated into a single chip, thus improving the detection sensitivity and facilitating chip operation. By applying the iHM, we demonstrate versatile magnetic assays. We measured the magnetic susceptibility and moments of MNPs using small sample amounts (∼10 pL), identified different MNP compositions in mixtures, and detected MNP-labeled single cells.

Controlled Domain Wall Pinning in Permalloy Nanowire by Nanoparticle Stray Fields

We report the results of experimental investigations of controlled domain wall (DW) pinning in a ferromagnetic nanowire (NW) by stray fields of two uniformly magnetized bistable ferromagnetic nanoparticles (NPs) placed on either side of the NW and elongated parallel to the NW axis. We show by magnetic force microscopy measurements that DW pinning strength essentially depends on the orientation of the NP magnetic moments relative to the NW magnetization and can reach 20 mT. We also performed micromagnetic simulations confirming the influence of the magnetostatic interaction of the DW with the NP stray fields on the pinning strength. The possible realization of logic cell with switchable logic function is discussed.

Magnetic properties of iron oxide-based nanoparticles: Study using Mössbauer spectroscopy with a high velocity resolution and magnetization measurements

We review the results of the study of magnetite, maghemite and nickel ferrite nanoparticles (NPs), applying for magnetic fluids, using Mössbauer spectroscopy with a high velocity resolution and magnetization measurements. The Mössbauer spectra of these NPs were fitted using a large number of magnetic sextets reflecting NPs complicity. The presence of polar molecules at the magnetite surface in magnetic fluid increases the NPs magnetic moment and the median hyperfine magnetic field. However, surface coating of maghemite NPs with dimeracptosuccinic acid decreases the median hyperfine magnetic field. An example of nickel ferrite NPs demonstrated a new physical model based on distribution of Ni2+ in the local microenvironment of Fe3+ which can explain a large number of magnetic sextets in the Mössbauer spectra measured with a high velocity resolution.

Tunability of Size and Magnetic Moment of Iron Oxide Nanoparticles Synthesized by Forced Hydrolysis

To utilize iron oxide nanoparticles in biomedical applications, a sufficient magnetic moment is crucial. Since this magnetic moment is directly proportional to the size of the superparamagnetic nanoparticles, synthesis methods of superparamagnetic iron oxide nanoparticles with tunable size are desirable. However, most existing protocols are plagued by several drawbacks. Presented here is a one-pot synthesis method resulting in monodisperse superparamagnetic iron oxide nanoparticles with a controllable size and magnetic moment using cost-effective reagents. The obtained nanoparticles were thoroughly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) measurements. Furthermore, the influence of the size on the magnetic moment of the nanoparticles is analyzed by superconducting quantum interference device (SQUID) magnetometry. To emphasize the potential use in biomedical applications, magnetic heating experiments were performed.

Phase composition and magnetic properties of iron oxide nanoparticles obtained by impulse electric discharge in water

The chemical composition and the magnetic properties of iron oxide nanoparticles obtained by impulse electric discharge in water are investigated. The phase composition of the Fe3O4, Fe2O3, and Fe nanoparticles is determined. By means of the nuclear magnatiec resonance (NMR) technique, the magnetic moments of the nanoparticles are determined. The magnetic moment of the spherical nanoparticles equals to 2.39 × 10–19 A m2, and that of the cubical ones is 4.56 × 10–19 A m2.