Synthesis of highly crystalline and monodisperse maghemite nanocrystallites without a size-selection process

Designed synthesis of Au/Ag/Pd trimetallic nanoparticle-based catalysts for Sonogashira coupling reactions

Pdnp and Pd containing trimetallic nanoparticles (tnp) are synthesized by chemical method with cetyltrimethylammonium bromide as the capping agent. Compositionally, four different tnp are prepared and the particle sizes are characterized by UV-vis spectra, HR-TEM, and XRD measurements. The catalytic activities of Pdnp and tnp are tested using the Sonogashira C-C coupling reaction. The product yield and recyclability of the recovered catalysts are studied. tnp (1:1:1) exhibited better catalysis than Pdnp, which may be due to the concerted electronic effects of the Au-Ag core onto the Pd shell atoms.

Synthesis, functionalization, and biomedical applications of multifunctional magnetic nanoparticles

Synthesis of multifunctional magnetic nanoparticles (MFMNPs) is one of the most active research areas in advanced materials. MFMNPs that have magnetic properties and other functionalities have been demonstrated to show great promise as multimodality imaging probes. Their multifunctional surfaces also allow rational conjugations of biological and drug molecules,making it possible to achieve target-specific diagnostics and therapeutics.This review fi rst outlines the synthesis of MNPs of metal oxides and alloy sand then focuses on recent developments in the fabrication of MFMNPs of core/shell, dumbbell, and composite hybrid type. It also summarizes the general strategies applied for NP surface functionalization. The review further highlights some exciting examples of these MFMNPs for multimodality imaging and for target-specific drug/gene delivery applications.

Biomedical Nanomagnetics: A Spin Through Possibilities in Imaging, Diagnostics, and Therapy

Biomedical nanomagnetics is a multidisciplinary area of research in science, engineering and medicine with broad applications in imaging, diagnostics and therapy. Recent developments offer exciting possibilities in personalized medicine provided a truly integrated approach, combining chemistry, materials science, physics, engineering, biology and medicine, is implemented. Emphasizing this perspective, here we address important issues for the rapid development of the field, i.e., magnetic behavior at the nanoscale with emphasis on the relaxation dynamics, synthesis and surface functionalization of nanoparticles and core-shell structures, biocompatibility and toxicity studies, biological constraints and opportunities, and in vivo and in vitro applications. Specifically, we discuss targeted drug delivery and triggered release, novel contrast agents for magnetic resonance imaging, cancer therapy using magnetic fluid hyperthermia, in vitro diagnostics and the emerging magnetic particle imaging technique, that is quantitative and sensitive enough to compete with established imaging methods. In addition, the physics of self-assembly, which is fundamental to both biology and the future development of nanoscience, is illustrated with magnetic nanoparticles. It is shown that various competing energies associated with self-assembly converge on the nanometer length scale and different assemblies can be tailored by varying particle size and size distribution. Throughout this paper, while we discuss our recent research in the broad context of the multidisciplinary literature, we hope to bridge the gap between related work in physics/chemistry/engineering and biology/medicine and, at the same time, present the essential concepts in the individual disciplines. This approach is essential as biomedical nanomagnetics moves into the next phase of innovative translational research with emphasis on development of quantitative in vivo imaging, targeted and triggered drug release, and image guided therapy including validation of delivery and therapy response.

Superparamagnetic iron oxide nanoparticles coated with galactose-carrying polymer for hepatocyte targeting

Our goal is to develop the functionalized superparamagnetic iron oxide nanoparticles (SPIONs) demonstrating the capacities to be delivered in liver specifically and to be dispersed in physiological environment stably. For this purpose, SPIONs were coated with polyvinylbenzyl-O-β-D-galactopyranosyl-D-gluconamide (PVLA) having galactose moieties to be recognized by asialoglycoprotein receptors (ASGP-R) on hepatocytes. For use as a control, we also prepared SPIONs coordinated with 2-pyrrolidone. The sizes, size distribution, structure, and coating of the nanoparticles were characterized by transmission electron microscopy (TEM), electrophoretic light scattering spectrophotometer (ELS), X-ray diffractometer (XRD), and Fourier transform infrared (FT-IR), respectively. Intracellular uptake of the PVLA-coated SPIONs was visualized by confocal laser scanning microscopy, and their hepatocyte-specific delivery was also investigated through magnetic resonance (MR) images of rat liver. MRI experimental results indicated that the PVLA-coated SPIONs possess the more specific accumulation property in liver compared with control, which suggests their potential utility as liver-targeting MRI contrast agent.

Organic phase synthesis of monodisperse iron oxide nanocrystals using iron chloride as precursor

Monodisperse iron oxide nanocrystals were synthesized by a simplified method using iron chloride as precursor. In the presence of Cl ions, the as-produced iron oxide nanocrystals preferred a cubic shape with {100} facets exposed. The function of halogens including Cl and Br ions on stabilizing {100} facets of spinel structured iron oxides, rather than the regulation of thermolysis kinetics and surfactants, was found influential on the shape control of nanocubes in this organic phase approach. The synthesis can be also extended for cobalt ferrite nanocubes and cobalt oxide polyhedrons.

Unique role of ionic liquid in microwave-assisted synthesis of monodisperse magnetite nanoparticles

A small amount of ionic liquid [bmim][BF(4)] was found to be an efficient aid for microwave heating of nonpolar dibenzyl ether in high temperature solution-phase synthesis of monodisperse magnetite nanoparticles. It was found to act as both microwave absorber and assistant stabilizer in the reactive process and was recovered and reused in successive reactions.

Cysteine-functionalized polyaspartic acid: a polymer for coating and bioconjugation of nanoparticles and quantum dots

We have synthesized a biocompatible polyaspartic acid-based polymer (molecular weight approximately 15,000-25,000) with cysteine on its backbone for use as a capping ligand for functionalized Au, Ag, and CdSe@ZnS nanoparticles. Nearly monodisperse, hydrophobic Au and Ag nanoparticles and CdSe@ZnS quantum dots were first prepared in organic solvents via conventional synthesis and then ligand exchanged to derive polymer-coated water-soluble nanoparticles. Multiple thiol groups in the polymer backbone conferred excellent protection against aggregation of the nanoparticles, and the carboxylic acid groups in the polymer provided the possibility of covalent binding with antibodies. Compared to the conventional thiol-based ligands, this polymer coating led to superior colloidal stability under the experimental conditions involved in the bioconjugation and purification steps. Goat antihuman-IgG (anti-h-IgG) and antimouse epidermal growth factor receptor (anti-m-EGFR) antibodies were conjugated with the polymer-coated nanoparticles and successfully applied to protein detection. This polymer coating exhibited minimal nonspecific interaction with cells and could be broadly applied to cell labeling.

Structural properties and magnetic interactions in Al3+ and Cr3+ co-substituted CoFe2O4 ferrite

A series of CoAlxCrxFe2−2xO4 systems (x = 0.1 to 0.5 in steps of x = 0.1) spinel ferrites have been synthesized successfully using wet chemical co-precipitation technique. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and magnetization measurements. The powder XRD patterns confirm the single phase spinel structure for the materials synthesized. X -ray diffraction measurements were performed to yield the lattice constant as function of the amount x corresponding to Al-Cr substitution. Lattice parameters, X-ray density, bulk density and particle size decrease whereas porosity increases with the increase in Al-Cr content, ‘x’. Infrared studies show two absorption bands at about 400 cm−1 and 600 cm−1 for octahedral and tetrahedral sites, respectively. Saturation magnetization decreases with the increase in Al-Cr content x. AC magnetic susceptibility measurements were carried out as a function of temperature to measure the Curie temperature, which was found to decrease with Al-Cr content x. The decrease of Curie temperature has been explained by A-B interaction.

Development and use of iron oxide nanoparticles (Part 1): Synthesis of iron oxide nanoparticles for MRI

Contrast agents, such as iron oxide, enhance MR images by altering the relaxation times of tissues in which the agent is present. They can also be used to label targeted molecular imaging probes. Unfortunately, no molecular imaging probe is currently available on the clinical MRI market. A promising platform for MRI contrast agent development is nanotechnology, where superparamagnetic iron oxide nanoparticles (SPIONS) are tailored for MR contrast enhancement, and/or for molecular imaging. SPIONs can be produced using a range of methods and the choice of method will be influenced by the characteristics most important for a particular application. In addition, the ability to attach molecular markers to SPIONS heralds their application in molecular imaging.There are many reviews on SPION synthesis for MRI; however, these tend to be targeted to a chemistry audience. The development of MRI contrast agents attracts experienced researchers from many fields including some researchers with little knowledge of medical imaging or MRI. This situation presents medical radiation practitioners with opportunities for involvement, collaboration or leadership in research depending on their level of commitment and their ability to learn. Medical radiation practitioners already possess a large portion of the understanding, knowledge and skills necessary for involvement in MRI development and molecular imaging. Their expertise in imaging technology, patient care and radiation safety provides them with skills that are directly applicable to research on the development and application of SPIONs and MRI.In this paper we argue that MRI SPIONs, currently limited to major research centres, will have widespread clinical use in the future. We believe that knowledge about this growing area of research provides an opportunity for medical radiation practitioners to enhance their specialised expertise to ensure best practice in a truly multi-disciplinary environment. This review outlines how and why SPIONs can be synthesised and examines their characteristics and limitations in the context of MR imaging.

Highly biocompatible and water-dispersible, amine functionalized magnetite nanoparticles, prepared by a low temperature, air-assisted polyol process: a new platform for bio-separation and diagnostics

A low temperature polyol process, based on glycolaldehyde mediated partial reduction of FeCl(3).6H(2)O at 120 degrees C in the presence of sodium acetate as an alkali source and 2, 2(')-(ethylenedioxy)-bis-(ethylamine) as an electrostatic stabilizer has been used for the gram-scale preparation of biocompatible, water-dispersible, amine functionalized magnetite nanoparticles (MNPs) with an average diameter of 6 +/- 0.75 nm. With a reasonably high magnetization (37.8 e.m.u.) and amine groups on the outer surface of the nanoparticles, we demonstrated the magnetic separation and concentration implications of these ultrasmall particles in immunoassay. MRI studies indicated that these nanoparticles had the desired relaxivity for T(2) contrast enhancement in vivo. In vitro biocompatibility, cell uptake and MR imaging studies established that these nanoparticles were safe in clinical dosages and by virtue of their ultrasmall sizes and positively charged surfaces could be easily internalized by cancer cells. All these positive attributes make these functional nanoparticles a promising platform for further in vitro and in vivo evaluations.

Optimized steric stabilization of aqueous ferrofluids and magnetic nanoparticles

The preparation and properties of an aqueous ferrofluid consisting of a concentrated (>65 wt %) dispersion of sterically stabilized superparamagnetic, iron oxide (maghemite) nanoparticles stable for several months at high ionic strength and over a broad pH range is described. The 6-8 nm diameter nanoparticles are individually coated with a short poly(acrylic acid)-b-poly(acrylamide) copolymer, designed to form the thinnest possible steric stabilizing layer while remaining strongly attached to the iron oxide surface over a wide range of nanoparticle concentrations. Thermogravimetric analysis yields an iron oxide content of 76 wt % in the dried particles, consistent with a dry polymer coating of approximately 1 nm in thickness, while the poly(acrylamide) chain length indicated by electrospray mass spectrometry is consistent with the 4-5 nm increase in the hydrodynamic radius observed by light scattering when the poly(acrylamide) stabilizing chains are solvated. Saturation magnetization experiments indicate nonmagnetic surface layers resulting from the strong chemical attachment of the poly(acrylic acid) block to the particle surface, also observed by Fourier transform infrared spectroscopy.

Nonaqueous synthesis and photoluminescence of ITO nanoparticles

SnO(2) has successfully been doped into octahedral In(2)O(3) nanoparticles using a high-temperature nonaqueous reaction. The resultant ITO nanoparticles exhibit a particle/crystal decrease in size, sphericity in morphology, and enhancement in photoluminescence.

Iron oxide-based nanomagnets in nanomedicine: fabrication and applications

Iron oxide-based nanomagnets have attracted a great deal of attention in nanomedicine over the past decade. Down to the nanoscale, superparamagnetic iron oxide nanoparticles can only be magnetized in the presence of an external magnetic field, which makes them capable of forming stable colloids in a physio-biological medium. Their superparamagnetic property, together with other intrinsic properties, such as low cytotoxicity, colloidal stability, and bioactive molecule conjugation capability, makes such nanomagnets ideal in both in-vitro and in-vivo biomedical applications. In this review, a chemical, physical, and biological synthetic approach to prepare iron oxide-based nanomagnets with different physicochemical properties was illustrated and compared. The growing interest in iron oxide-based nanomagnets with multifunctionalities was explored in cancer diagnostics and treatment, focusing on their combined roles in a magnetic resonance contrast agent, hyperthermia, and magnetic force assisted drug delivery. Iron oxides as magnetic carriers in gene therapy were reviewed with a focus on the sophisticated design and construction of magnetic vectors. Finally, the iron oxide-based nanomagnet also represents a very promising tool in particle/cell interfacing in controlling cellular functionalities, such as adhesion, proliferation, differentiation, and cell patterning, in stem cell therapy and tissue engineering applications.

A nonaqueous approach to the preparation of iron phosphide nanowires

Previous preparation of iron phosphide nanowires usually employed toxic and unstable iron carbonyl compounds as precursor. In this study, we demonstrate that iron phosphide nanowires can be synthesized via a facile nonaqueous chemical route that utilizes a commonly available iron precursor, iron (III) acetylacetonate. In the synthesis, trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) have been used as surfactants, and oleylamine has been used as solvent. The crystalline structure and morphology of the as-synthesized products were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The obtained iron phosphide nanowires have a typical width of ~16 nm and a length of several hundred nanometers. Structural and compositional characterization reveals a hexagonal Fe2P crystalline phase. The morphology of as-synthesized products is greatly influenced by the ratio of TOP/TOPO. The presence of TOPO has been found to be essential for the growth of high-quality iron phosphide nanowires. Magnetic measurements reveal ferromagnetic characteristics, and hysteresis behaviors below the blocking temperature have been observed.

The use of microgel iron oxide nanoparticles in studies of magnetic resonance relaxation and endothelial progenitor cell labelling

In vivo tracking of stem cells after transplantation is crucial for understanding cell-fate and therapeutic efficacy. By labelling stem cells with magnetic particles, they can be tracked by Magnetic Resonance Imaging (MRI). We previously demonstrated that microgel iron oxide nanoparticle (MGIO) provide superior tracking sensitivity over commercially available particles. Here, we describe the synthesis of MGIO and report on their morphology, hydrodynamic diameters (87-766 nm), iron oxide weight content (up to 82%) and magnetization characteristics (M(s)=52.9 Am(2)/kg, M(R)=0.061 Am(2)/kg and H(c)=0.672 A/m). Their MR relaxation characteristics are comparable to those of theoretical models and represent the first such correlation between model and real particles of varying diameters. A labelling study of primary endothelial progenitor cells also confirms that MGIO is an efficient label regardless of cell type. The facile synthesis of MGIO makes it a useful tool for the studying of relaxation induced by magnetic particles and cellular tracking by MRI.

Porous Silicon—A Versatile Host Material

This work reviews the use of porous silicon (PS) as a nanomaterial which is extensively investigated and utilized for various applications, e.g., in the fields of optics, sensor technology and biomedicine. Furthermore the combination of PS with one or more materials which are also nanostructured due to their deposition within the porous matrix is discussed. Such nanocompounds offer a broad avenue of new and interesting properties depending on the kind of involved materials as well as on their morphology. The filling of the pores performed by electroless or electrochemical deposition is described, whereas different morphologies, reaching from micro- to macro pores are utilized as host material which can be self-organized or fabricated by prestructuring. For metal-deposition within the porous structures, both ferromagnetic and non-magnetic metals are used. Emphasis will be put on self-arranged mesoporous silicon, offering a quasi-regular pore arrangement, employed as template for filling with ferromagnetic metals. By varying the deposition parameters the precipitation of the metal structures within the pores can be tuned in geometry and spatial distribution leading to samples with desired magnetic properties. The correlation between morphology and magnetic behaviour of such semiconducting/magnetic systems will be determined. Porous silicon and its combination with a variety of filling materials leads to nanocomposites with specific physical properties caused by the nanometric size and give rise to a multiplicity of potential applications in spintronics, magnetic and magneto-optic devices, nutritional food additives as well as drug delivery.

Experimental validation of proton transverse relaxivity models for superparamagnetic nanoparticle MRI contrast agents

Analytical models of proton transverse relaxation rate enhancement by magnetic nanoparticles were tested by making measurements on model experimental systems in a field of 1.4 T. Proton relaxivities were measured for five aqueous suspensions of iron oxide (maghemite) nanoparticles with nominal mean particle sizes of 6, 8, 10, 11, and 13 nm. Proton relaxivity increased with mean particle size ranging from 13 s(-1) mM Fe(-1) for the 6 nm sample, up to 254 s(-1) mM Fe(-1) for the 13 nm sample. A strong correlation between the measured and predicted values of the relaxivity was observed, with the predicted values being consistently higher than the measured values. The results indicate that the models give a reasonable agreement with experimental results and hence can be used as the basis for the design of new magnetic resonance imaging contrast and labelling agents.

Progress of nanocrystalline growth kinetics based on oriented attachment

The crystal growth mechanism, kinetics, and microstructure development play a fundamental role in tailoring the materials with controllable sizes and morphologies. The classical crystal growth kinetics-Ostwald ripening (OR) theory is usually used to explain the diffusion-controlled crystal growth process, in which larger particles grow at the expense of smaller particles. In nanoscale systems, another significant mechanism named "oriented attachment (OA)" was found, where nanoparticles with common crystallographic orientations directly combine together to form larger ones. Comparing with the classical atom/molecular-mediated crystallization pathway, the OA mechanism shows its specific characteristics and roles in the process of nanocrystal growth. In recent years, the OA mechanism has been widely reported in preparing low-dimension nanostructural materials and reveals remarkable effects on directing and mediating the self-assembly of nanocrystals. Currently, the interests are more focused on the investigation of its role rather than the comprehensive insight of the mechanism and kinetics. The inner complicacy of crystal growth and the occurrence of coexisting mechanisms lead to the difficulty and lack of understanding this growth process by the OA mechanism.In this context, we review the progress of the OA mechanism and its impact on materials science, and especially highlight the OA-based growth kinetics aiming to achieve a further understanding of this crystal growth route. To explore the OA-limited growth, the influence of the OR mechanism needs to be eliminated. The introduction of strong surface adsorption was reported as the effective solution to hinder OR from occurring and facilitate the exclusive OA growth stage. A detailed survey of the nanocrystal growth kinetics under the effect of surface adsorption was presented and summarized. Moreover, the development of OA kinetic models was systematically generalized, in which the "molecular-like" kinetic models were built to take the OA nanocrystal growth behavior as the collision and reaction between molecules. The development of OA growth kinetics can provide a sufficient understanding of crystal growth, and the awareness of underlying factors in the growth will offer promising guidance on how to control the size distribution and shape development of nanostructural materials.

Surface Engineering of Core/Shell Iron/Iron Oxide Nanoparticles from Microemulsions for Hyperthermia

This paper describes the synthesis and surface engineering of core/shell-type iron/iron oxide nanoparticles for magnetic hyperthermia cancer therapy. Iron/iron oxide nanoparticles were synthesized from microemulsions of NaBH(4) and FeCl(3), followed by surface modification in which a thin hydrophobic hexamethyldisilazane layer - used to protect the iron core - replaced the CTAB coating on the particles. Phosphatidylcholine was then assembled on the nanoparticle surface. The resulting nanocomposite particles have a biocompatible surface and show good stability in both air and aqueous solution. Compared to iron oxide nanoparticles, the nanocomposites show much better heating in an alternating magnetic field. They are good candidates for both hyperthermia and magnetic resonance imaging applications.

Magnetic nanoparticles for biomedical NMR-based diagnostics

Rapid and accurate measurements of protein biomarkers, pathogens and cells in biological samples could provide useful information for early disease diagnosis, treatment monitoring, and design of personalized medicine. In general, biological samples have only negligible magnetic susceptibility. Thus, using magnetic nanoparticles for biosensing not only enhances sensitivity but also effectively reduces sample preparation needs. This review focuses on the use of magnetic nanoparticles for in vitro detection of biomolecules and cells based on magnetic resonance effects. This detection platform, termed diagnostic magnetic resonance (DMR), exploits magnetic nanoparticles as proximity sensors, which modulate the spin-spin relaxation time of water molecules surrounding molecularly-targeted nanoparticles. By developing more effective magnetic nanoparticle biosensors, DMR detection limits for various target moieties have been considerably improved over the last few years. Already, a library of magnetic nanoparticles has been developed, in which a wide range of targets, including DNA/mRNA, proteins, small molecules/drugs, bacteria, and tumor cells, have been quantified. More recently, the capabilities of DMR technology have been further advanced with new developments such as miniaturized nuclear magnetic resonance detectors, better magnetic nanoparticles and novel conjugational methods. These developments have enabled parallel and sensitive measurements to be made from small volume samples. Thus, the DMR technology is a highly attractive platform for portable, low-cost, and efficient biomolecular detection within a biomedical setting.

Polymeric micelles: polyethylene glycol-phosphatidylethanolamine (PEG-PE)-based micelles as an example

One of the renowned nanosized pharmaceutical carriers for delivery of poorly soluble drugs, especially, in cancer, is micelles, which are self-assembled colloidal particles with a hydrophobic core and hydrophilic shell. Among the micelle-forming compounds, micelles made of polyethylene glycol-phosphatidylethanolamine (PEG-PE) have gained more attention due to some attractive properties such as good stability, longevity, and ability to accumulate in the areas with an abnormal vasculature via the enhanced permeability and retention effect (into the areas with leaky vasculature, such as tumors). Additionally these micelles can be made "targeted" by attaching specific targeting ligand molecules to the micelle surface or can be comprised of stimuli-responsive amphiphilic block copolymers. Addition of second component such as surfactant or another hydrophobic material to the main micelle forming material further improves the solubilizing capacity of micelles without compromising their stability. Micelles carrying various contrast agents may become the imaging agents of choice in different imaging modalities. Here, we have discussed various protocols for preparation and evaluation of PEG-PE-based micelles.

Quasicrystalline order in self-assembled binary nanoparticle superlattices

The discovery of quasicrystals in 1984 changed our view of ordered solids as periodic structures and introduced new long-range-ordered phases lacking any translational symmetry. Quasicrystals permit symmetry operations forbidden in classical crystallography, for example five-, eight-, ten- and 12-fold rotations, yet have sharp diffraction peaks. Intermetallic compounds have been observed to form both metastable and energetically stabilized quasicrystals; quasicrystalline order has also been reported for the tantalum telluride phase with an approximate Ta(1.6)Te composition. Later, quasicrystals were discovered in soft matter, namely supramolecular structures of organic dendrimers and tri-block copolymers, and micrometre-sized colloidal spheres have been arranged into quasicrystalline arrays by using intense laser beams that create quasi-periodic optical standing-wave patterns. Here we show that colloidal inorganic nanoparticles can self-assemble into binary aperiodic superlattices. We observe formation of assemblies with dodecagonal quasicrystalline order in different binary nanoparticle systems: 13.4-nm Fe(2)O(3) and 5-nm Au nanocrystals, 12.6-nm Fe(3)O(4) and 4.7-nm Au nanocrystals, and 9-nm PbS and 3-nm Pd nanocrystals. Such compositional flexibility indicates that the formation of quasicrystalline nanoparticle assemblies does not require a unique combination of interparticle interactions, but is a general sphere-packing phenomenon governed by the entropy and simple interparticle potentials. We also find that dodecagonal quasicrystalline superlattices can form low-defect interfaces with ordinary crystalline binary superlattices, using fragments of (3(3).4(2)) Archimedean tiling as the 'wetting layer' between the periodic and aperiodic phases.

Chemically synthesized FePt nanoparticles with controlled particle size, shape and composition

Monodisperse Fe-Pt nanoparticles have been prepared by thermal decomposition of iron pentacarbonyl [Fe(CO)5] and reduction of platinum acetylacetonate [Pt(acac)2] with dibenzyl ether in the presence of oleic acid and oleyl amine. The particle composition was adjusted by changing the Fe(CO)5/Pt(acac)2 molar ratio while fixing the Pt(acac)2 amount. The size of FePt nanoparticles was tuned by controlling the injection temperature of the iron precursor. The low injection temperature of precursors and the usage of surfactants as a reaction solvent, together with a slow heating to a low refluxing temperature, were found to be the key parameters for the formation of cubic nanoparticles. Nanorods were formed by simply adjusting the injection time of the surfactants. The as-made nanoparticles had a low coercivity, which was increased to 7 kOe when annealed at 800 degrees C for 1 h.