Theoretical assessment of FePt nanoparticles as heating elements for magnetic hyperthermia

FePt magnetic nanoparticles (MNPs) are expected to be a high-performance nanoheater for magnetic hyperthermia because of their high Curie temperature, high saturation magnetization, and high chemical stability. Here, we present a theoretical performance assessment of chemically disordered fcc-phase FePt MNPs. We calculate heat generation and heat transfer in the tissue when an MNP-loaded tumor is placed on an external alternating magnetic field. For comparison, we estimate the performances of magnetite, maghemite, FeCo, and L1/sub 0/-phase FePt MNPs. We find that an fcc FePt MNP has a superior ability in magnetic hyperthermia.     

Influence of particle size on spin switching properties and magnetoelectric coupling in SmFeO<Subscript>3</Subscript>

Controlling the magnetic properties of a material is of great importance for spintronics and magnetoelastic devices. We studied effect of reduced particle size on structural, dielectric and magnetic properties of SmFeO₃ nanoparticles prepared by co-precipitation method (SFO-C) and by combustion (SFO-S). Reduced particle size modified interesting magnetic features of SmFeO₃. Temperature dependent magnetic study reveal significant enhancement in magnetization reversal temperature and drop in spin reorientation transition temperature. The signature of spin reorientation transition for SFO-C (~?300 nm) is marked at ~?450 K, while this temperature drops down to ~?400 K for SFO-C (~?50 nm). The magnetization reversal temperature is achieved at 30.5 K for SFO-C, much higher than 4 K, reported for the single crystal and bulk SmFeO₃. The presence significant anomalies in the temperature dependent dielectric behavior of SmFeO₃ samples across spin reorientation transition temperature indicate magneto electrical coupling. Strong exchange–bias effect is observed at low temperature for both the samples. The lowering of spin reorientation/switching transition temperature due to reduction in particle size and the signature of magnetoelectric coupling at this temperature are useful for room temperature devices. The observed experimental results establish that the spin switching properties of SmFeO₃ can be modified for practical applications in devices.     

Rotation of the magnetization vector of a monodomain particle under the action of a high-frequency field pulse

We obtained a numerical solution of the modified Hilbert equation describing rotation of the magnetization vector in a high-frequency field of large amplitude. Based on this solution, we have studied rotation of the magnetization vector of a spherical ferromagnetic monodomain particle, possessing a cubic anisotropy, from the direction parallel to an easy magnetization axis to the perpendicular direction under the action of a high-frequency magnetic field pulse. The amplitudes and the interval of frequencies of the magnetic field capable of rotating the particle magnetization vector are determined.     

Dominant dipolar interaction and glassy magnetic behaviour in polymer-coated magnetite nanoparticles

The static and dynamic properties of magnetization have been investigated for polymer-coated magnetite nanoparticles with sizes from 5 to 15?nm. The analysis of the temperature dependence of zero-field-cooled magnetization indicates that the effective anisotropy constant is found to increase with the decrease of particle size, which is ascribed to the increase of surface anisotropy. The relaxation of the remanent magnetization clearly shows the signature of dominant dipolar interparticle interaction. The dynamics of magnetization also indicates the signature of glassy magnetic behaviour. The memory effect in the temperature dependence of field-cooled magnetization is noticed, which is inconsistent with the glassy magnetic behaviour.     

Computational modeling of magnetic nanoparticle targeting to stent surface under high gradient field

A multi-physics model was developed to study the delivery of magnetic nanoparticles (MNPs) to the stent-implanted region under an external magnetic field. The model is firstly validated by experimental work in literature. Then, effects of external magnetic field strength, magnetic particle size, and flow velocity on MNPs’ targeting and binding have been analyzed through a parametric study. Two new dimensionless numbers were introduced to characterize relative effects of Brownian motion, magnetic force induced particle motion, and convective blood flow on MNPs motion. It was found that larger magnetic field strength, bigger MNP size, and slower flow velocity increase the capture efficiency of MNPs. The distribution of captured MNPs on the vessel along axial and azimuthal directions was also discussed. Results showed that the MNPs density decreased exponentially along axial direction after one-dose injection while it was uniform along azimuthal direction in the whole stented region (averaged over all sections). For the beginning section of the stented region, the density ratio distribution of captured MNPs along azimuthal direction is center-symmetrical, corresponding to the center-symmetrical distribution of magnetic force in that section. Two different generation mechanisms are revealed to form four main attraction regions. These results could serve as guidelines to design a better magnetic drug delivery system.     

Ferromagnetic and Charge-Ordered Phases in (Nd, Na)?CMn?CO Compounds

Polycrystalline Nd_1?x Na _x MnO₃ ( $x=0.05\mbox{--} 0.20$ ) compounds were prepared in single-phase form with a Pbnm space group. Paramagnetic to ferromagnetic transitions were observed up to a doping concentration of 15% with a maximum T _C of 113?K. The x=0.20 sample exhibits a charge order transition at 180?K, with a distinct behavior in magnetization versus field curve. The magnetization versus temperature plot of all these materials exhibits an anomaly at around 40?K, with a signature of spin-glass like behavior. The x=0.10 sample is found to exhibit a maximum spontaneous magnetization value of 3.1?? _B at 20?K. The magnetization data could be analyzed based on the Brillouin function model, by accounting for the ferromagnetic interaction. The effective spin contribution of 3d electrons for the double-exchange ferromagnetic interaction and the value of magnetic spin-canting angles were estimated. The measured magnetization is explained on the basis of competing magnetic interaction due to spin-canting. The charge order quenching and the first-order transition from the charge-ordered to ferromagnetic phase are observed for a threshold field of 3?T at 12?K. The electrical resistivity of the above samples exhibits insulating behavior.     

Synthesis and Magnetic Properties of Mn<Subscript>12</Subscript>-Based Single Molecular Magnets with Benzene and Pentafluorobenzene Carboxylate Ligands

We report on the synthesis and magnetic properties of Mn₁₂-based single molecular magnets (SMMs) with benzene and pentafluorobenzene carboxylate ligands. The changes in ligand structure are shown to have a decisive effect on the magnetic properties of the complexes produced. The compound with benzene demonstrates an unusual magnetic behavior, namely, temperature dependencies of magnetization taken under the zero-field-cooled and field-cooled conditions are split below 10 K and furthermore remnant magnetization and coercive force remain nonzero in this temperature range. In contrast, the compound with pentafluorobenzene displays the customary signatures of the blocking temperature at 3 K. The effect of ligand substitution was theoretically studied within the local density approximation taking into account on-site Coloumb repulsion. Calculation results confirm that the electronic structure and the magnetic exchange interactions between different Mn atoms strongly depend on the type of ligand.     

Effect of Synthesis Parameters on the Properties of Superparamagnetic Iron Oxide Nanoparticles

Iron oxide nanoparticles were coprecipitated in air medium using different sodium hydroxide (NaOH) concentrations, and their structural and magnetic properties were studied. It was observed that the precipitation of superparamagnetic iron oxide nanoparticles could be achieved above a critical NaOH concentration. This was followed by the investigation of the effect of the stirring rate on the structural and magnetic properties of the nanoparticles precipitated at 8.5?M NaOH and over. Morphological observation made by a transmission electron microscope (TEM) showed that the particle size of iron oxide nanoparticles was around 7.5?nm. Magnetization curves measured by a vibrating sample magnetometer showed zero coercivity indicating that the samples are superparamagnetic and the highest saturation magnetization (70.4?emu/g) was obtained at the stirring rate of 1100?rpm. The mean particle sizes of iron oxide nanoparticles calculated from the magnetization data are found to be consistent with the particle sizes obtained from the TEM images.     

Preparation of New Composite Magnetocaloric Compounds by Modifying the Annealing Temperature of La0.8Ca0.2?x □ x MnO3 Perovskite

In this paper, a new method to broaden the range of the magnetic refrigeration temperature by changing the annealing temperature was proposed. Series of La_0.8Ca_0.2?x ?? _x MnO₃(0.00??x??0.20) compounds were prepared by solid-state reaction and annealed firstly at a temperature of 1473 K (S1) and then at 1073 K (S2). Morphologic and structural studies have revealed that the decrease of the annealing temperature modifies the grain size and the structure of these compounds. The magnetic measurements have shown that the annealing at low temperature (1073 K) increases the magnetization and enhances the one-electron bandwidth, which induces an increase of the Curie temperature for 183 K (S1) to 241 K (S2) for the x=0.00 sample. The magnetocaloric investigation has exposed that the decrease of the annealing temperature induces a change from a second-order magnetic phase transition to first-order one for S1 and S2 compounds, respectively. Also, we have found that the Relative Cooling Power (RCP) factor remains almost constant as a function of calcium-deficiency concentration (x) and the annealing temperature. Finally, we have deduced that we can use composite magnetocaloric compounds, exploiting a mixing of the same compounds annealed at two different temperatures (1473 K; S1) and (1073?K; S2), for refrigeration over the temperature range 175?C264?K.     

Effect of Mn doping concentration on structural,vibrational and magnetic properties of NiO nanoparticles

The Ni_1?xMn_xO (x?=?0.00, 0.02, 0.04 and 0.06) nanoparticles were synthesized by chemical precipitation route followed by calcination at 500?°C for 4?h. The prepared samples were characterized by energy dispersive analysis of X-rays (EDAX), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Rietveld refinement of XRD data confirms the structural phase purity and XRD patterns are well indexed to NaCl like rock salt fcc crystal structure with Fm-3m space group. The particle size of Mn doped samples is found to be less than that of pure NiO sample. However, the particle size increases slightly on increasing the Mn concentration due to surface/grain boundary diffusion. The vibrational properties of the synthesized nanoparticles were investigated by Raman and FT-IR spectroscopy. The results of room temperature magnetization (M-H) and temperature dependent magnetization (M-T) measurements are explained with a core-shell model. The synthesized nanoparticles show weak ferromagnetic and super-paramagnetic like behavior at room temperature.     

Wet-chemical green synthesis of L-lysine amino acid stabilized biocompatible iron-oxide magnetic nanoparticles

In this paper, we report a novel method for the synthesis of L-Lysine (lys) amino acid coated maghemite (gamma-Fe2O3) magnetic nanoparticles (MNPs). The facile and cost effective method permitted preparation of the high-quality superparamagnetic gamma-Fe2O3 MNPs with hydrophilic and biocompatible nature. For this work, first we synthesized magnetite phase Fe3O4/lys by wet chemical method and oxidized to y-Fe2O3 in controlled oxidizing environment, as evidenced by XRD and VSM magnetometry. The crystallite size and magnetization of gamma-Fe2O3/lys MNPs was found to be 14.5 nm, 40.6 emu/gm respectively. The surface functionalization by L-lysine amino acid and metal-ligand bonding was also confirmed by FTIR spectroscopy. The hydrodynamic diameter, colloidal stability and surface charge on MNPs were characterized by DLS and zeta potential analyser.     

Formulation and characterization of novel temperature sensitive polymer-coated magnetic nanoparticles

The objective of this research was to develop novel polymer coated magnetic nanoparticles for controlled drug delivery applications. To form these novel nanoparticles, silane-coated magnetic nanoparticles (MNPs) were used as a template for a free radial polymerization of three monomers, N-isopropylacrylamide, acrylamide, and allylamine (NIPA-AAm-AH), on the surface of MNPs. Transmission electron microscope results indicated that the size of the NIPA-AAm-AH coated MNPs was approximately 100 nm. To investigate the chemical composition and chemical state of our nanoparticles, FTIR and XPS were used. Results from chemical analysis illustrated the presence of the constituent functional groups of the NIPA-AAm-AH coated MNPs. In addition, the magnetic properties of different layers on the MNPs, analyzed by SQUID, indicated a decrease in saturation magnetization after each layer of coating. The nanoparticles were successfully conjugated to fluorescent PEG to prolong their circulating half life. Furthermore, bovine serum albumin (BSA) was used in order to investigate the protein release profile of the nanoparticles as a function of the temperature. The protein release profile indicated that the NIPA-AAm-AH coated MNPs have a significantly higher percent release at 41 degrees C compared to those of 4 degrees C and 37 degrees C, which demonstrates their temperature sensitivity. In the future, the release profile of therapeutic drugs from nanoparticles at various temperatures and pHs as well as targeted capability of the synthesized nanoparticles for possible applications in controlled and targeted delivery will be investigated.     

Heat Transfer and Magnetovortical Antiresonance of a Ferrofluid with a Rotating Magnetic Field

We investigate theoretically a ferrofluid in the presence of a rotating magnetic field using a phenomenological approach based on a equation of motion for the magnetization. We verify that the heating rates of the system display a heat transfer between the host liquid and the magnetic nanoparticles (MNPs), with symmetric profiles dependent on the vorticity value. As a result, the total heating rate reveals a magnetovortical antiresonance and characterizes the suppression of the dissipation.     

The role of aggregation of ferrite nanoparticles on their magnetic properties

We have studied the magnetic properties of aggregates of Mn0.5Zn0.5Gd(x)Fe(2-x)O4 ferrite nanoparticles, with x = 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.20. The scanning electron microscopy micrographs show significant aggregation of the nanoparticles in all samples. Zero field cooled and field cooled magnetization measurements were conducted on all samples from 400 K down to 5 K. Most zero field cooled curves were found to exhibit the usual behavior but with wide peaked regions. For some x values, the field cooled magnetization was found to increase slowly with decreasing temperature, and becomes nearly constant at low temperatures. The measurements of magnetization versus applied magnetic field were conducted on all samples at 5 K and 305 K in the field range from -15000 to 15000 Oe. At 305 K the magnetization for all samples was observed to saturate, while at 5 K the magnetization did not reach saturation for some values of x. The saturation magnetization values were suggested to be proportional to the size of particles. These results were discussed and suggested to be due to the inter-particle dipolar and exchange interactions between the particles in the aggregates, the large particle size distribution and the surface magnetization effects.     

Numerical study of temperature distribution in a spherical tissue in magnetic fluid hyperthermia using lattice Boltzmann method

This work applies a three-dimensional lattice Boltzmann method (LBM), to solve the Pennes bio-heat equation (BHE), in order to predict the temperature distribution in a spherical tissue, with blood perfusion, metabolism and magnetic nanoparticles (MNPs) heat sources, during magnetic fluid hyperthermia (MFH). So, heat dissipation of MNPs under an alternating magnetic field has been studied and effect of different factors such as induction and frequency of magnetic field and volume fraction of MNPs has been investigated. Then, effect of MNPs dispersion on temperature distribution inside tumor and its surrounding healthy tissue has been shown. Also, effect of blood perfusion, thermal conductivity of tumor, frequency and amplitude of magnetic field on temperature distribution has been explained. Results show that the LBM has a good accuracy to solve the bio-heat transfer problems.     

Three-Dimensional Model for Determining Inhomogeneous Thermal Dosage in a Liver Tumor During Arterial Embolization Hyperthermia Incorporating Magnetic Nanoparticles

Hyperthermia treatment incorporating magnetic nanoparticles (MNPs) is a hopeful therapy for cancers. Acquiring information about the MNPs' deposition in tumor tissues and modeling magnetic heating in vivo are essential for successful treatment. In this paper, we discuss the inhomogeneous heat generation by MNPs distributed heterogeneously in a liver tumor during arterial embolization hyperthermia (AEH) treatments. In order to more accurately simulate the temperature elevation for an AEH treatment plan, we conducted the following experiments. First, we detected the distribution of magnetic field intensity in the aperture of a ferrite-core applicator. We found that attenuation of the magnetic field focuses mainly on the vertical distance of the aperture, which makes MNPs in tissues have different power loss along the lognitudinal axis. Second, we prepared 20 nm monodisperse lipiodol-soluble MNPs and injected super-selectively through the micro-catheter into the arteries of a rabbit with a VX-2 liver tumor. By histological cuts of the investigated specimen, as well as computed tomography (CT), we found MNPs mainly concentrated on the tumor periphery. Last, from the experimental information, we established a new model for simulating the increasing temperature in the liver tumor based on our inhomogeneous interior-heat-source analysis (IIA). We also compared the simulated results with the two types of homogeneous models. The results showed that IIA gives significantly different results from those for a homogeneous model and thus is preferable when an accurate treatment plan is required during AEH.      

The effect of the strength and direction of magnetic field on the assembly of magnetic nanoparticles into higher structures

The self-assembly of magnetic nanoparticles into higher-order organizations upon external magnetic stimulation has critical importance for the fabrication of discrete microstructures. In this study, the tuning of self-assembly behavior of magnetic Fe3O4 nanoparticles (MNPs), with an average size of 6 nm, under the enhanced magnetic force upon changing the applied field strength and direction is explored. Upon evaporation of the solvent where the MNPs are suspended, formation of particular micrometer sized structures is achieved with a surface constructed from sub-micrometer size magnetic beads in between the applied magnetic field and MNPs. In this study, three different surfaces fabricated using sub-micrometer size magnetic beads in between the applied magnetic field and MNPs are used and the effect of the template pattern, applied field strength and direction are explored.     

Thermal analysis in the rat glioma model during directly multipoint injection hyperthermia incorporating magnetic nanoparticles

Hyperthermia incorporating magnetic nanoparticles (MNPs) is a hopeful therapy to cancers and steps into clinical tests at present. However, the clinical plan of MNPs deposition in tumors, especially applied for directly multipoint injection hyperthermia (DMIH), and the information of temperature rise in tumors by DMIH is lack of studied. In this paper, we mainly discussed thermal distributions induced by MNPs in the rat brain tumors during DMIH. Due to limited experimental measurement for detecting thermal dose of tumors, and in order to acquire optimized results of temperature distributions clinically needed, we designed the thermal model in which three types of MNPs injection for hyperthermia treatments were simulated. The simulated results showed that MNPs injection plan played an important role in determining thermal distribution, as well as the overall dose of MNPs injected. We found that as injected points enhanced, the difference of temperature in the whole tumor volume decreased. Moreover, from temperature detecting data by Fiber Optic Temperature Sensors (FOTSs) in glioma bearing rats during MNPs hyperthermia, we found the temperature errors by FOTSs reduced as the number of points injected enhanced. Finally, the results showed that the simulations are preferable and the optimized plans of the numbers and spatial positions of MNPs points injected are essential during direct injection hyperthermia.     

Synthesis and magnetic properties of nanocolumnar nickel films deposited in argon-nitrogen atmosphere

Ferromagnetic nickel films with a structure comprising nanocolumns grown perpendicular to a substrate have been obtained by magnetron sputtering of a nickel target in argon atmosphere containing 2 vol % nitrogen. Measurements of X-ray diffraction and investigation of magnetic properties showed that the obtained films consist of a solid solution of nitrogen in nickel. The saturation magnetization of the films is 1.5?C2 times smaller and their Curie temperature is 30 K lower than the corresponding values for pure nickel. The film material exhibits a dimensional effect: as the grain size decreases below 10 nm, the magnetization sharply drops; at a grain size of 0.5 nm, the film possesses no magnetic order.     

Size-dependent properties of magnetoferritin

We report a detailed experimental study of maghemite nanoparticles, with sizes ranging from 1.6 to 6 nm, synthesized inside a biological mould of apoferritin. The structural characterization of the inorganic cores, using TEM and x-ray diffraction, reveals a low degree of crystalline order, possibly arising from the nucleation and growth of multiple domains inside each molecule. We have also investigated the molecular structure by means of atomic force microscopy in liquid. We find that the synthesis of nanoparticles inside apoferritin leads to a small, but measurable, decrease in the external diameter of the protein, probably associated with conformational changes. The magnetic response of the maghemite cores has been studied by a combination of techniques, including ac susceptibility, dc magnetization and M?ssbauer spectroscopy. From the equilibrium magnetic response, we have determined the distribution of magnetic moments per molecule. The results show highly reduced magnetic moments. This effect cannot be ascribed solely to the canting of spins located at the particle surface but, instead, it suggests that magnetoferritin cores have a highly disordered magnetic structure in which the contributions of different domains compensate each other. Finally, we have also determined, for each sample, the distribution of the activation energies required for the magnetization reversal and, from this, the size-dependent magnetic anisotropy constant K. We find that K is enormously enhanced with respect to the maghemite bulk value and that it increases with decreasing size. The M?ssbauer spectra suggest that low-symmetry atomic sites, probably located at the particle surface and at the interfaces between different crystalline domains, are the likely source of the enhanced magnetic anisotropy.