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Tuning the magnetic properties of Zn1-xCoxO films
We compare the magnetic properties of two types of Co-doped ZnO films grown on sapphire with distinct structural quality. SQUID magnetometry as well as element-specific synchrotron studies reveal pure paramagnetic behavior for the samples with the highest structural quality, whereas samples with reduced structural quality exhibit superparamagnetic blocking behavior. In this sample signatures of phase separation are detected by X-ray diffraction and X-ray linear dichroism which accounts for the superparamagnetic blocking.
Lignocellulose-stabilized iron-palladium nanomagnetic biocomposites
In this study we report the synthesis and characterization of superparamagnetic Fe-Pd (1–75 at.% Fe) nanomagnets grown within a lignocellulose fiber matrix for future advanced material applications. The small (~5 nm diameter) Fe-Pd nanoparticles are crystalline with spherical shape and evenly dispersed throughout the lignocellulose support while preserving the structure of the biopolymer matrix. Material characterization of the as-formed biocomposites confirms primarily zero-valent Pd-Fe alloy with a thin surface oxide layer. Normal superparamagnetic behavior consistent with extremely small nanoparticle size is measured, including increasing measured blocking temperature with increasing Fe concentration. Finally, important mass loading effects of metallic nanoparticles within the lignocellulose matrix are measured and discussed.
Charge ordering and multiferroicity in Fe{sub 3}BO{sub 5} and Fe{sub 2}MnBO{sub 5} oxyborates
The comparison of Fe{sub 3}BO{sub 5} and Fe{sub 2}MnBO{sub 5} reveals that the 2Fe{sup 2+}: Fe{sup 3+} charge ordering of the former is suppressed in the latter. Spin dynamics probed by ac susceptibility are strongly affected by the substitution, inducing superparamagnetism at low temperature in Fe{sub 2}MnBO{sub 5}. Interestingly, for both oxyborates, glassiness is observed in the dielectric properties at low temperature, but only Fe{sub 3}BO{sub 5} shows a magnetodielectric effect close to its lower magnetic transition. A change in the electrical polarization, measured by pyroelectric current integration, is observed in Fe{sub 3}BO{sub 5} and is even more pronounced in Fe{sub 2}MnBO{sub 5}. Such results suggest that these oxyborates behave like antiferromagnetic relaxor ferroelectrics. These features are proposed to be related to the distribution of the species (Fe{sup 3+}, Fe{sup 2+} and Mn{sup 2+}) over the four transition metal sites forming the ludwigite structure. - Graphical abstract: 90 K [010] electron diffraction patterns of Fe{sub 3}BO{sub 5}. The yellow arrows in the pattern indicate the extra-spots corresponding to the superstructure induced by the charge ordering. - Highlights: • The TEM (ED) study of the Fe{sub 3}BO{sub 5} oxyborate at 90 K reveals a superstructure related to a Fe{sup 2+}/Fe{sup 3+} ordering. • The Fe{sub 2}MnBO{sub 5}, Mn-substituted counterpart, does not show such ordering. • Our magnetic and electric measurements demonstrate that these magnetic ferrites exhibit glassiness in their charges (relaxor-type) with additional superparamagnetism at low T for Fe{sub 2}MnBO{sub 5} and magnetodielectric coupling near T{sub N2}=72 K in Fe{sub 3}BO{sub 5}. • The pyroelectric measurements confirm the existence of a ferroelectric behavior in these antiferromagnets. Accordingly, our results open the route to the study of other large class of the M{sub 2}{sup 2+}M’{sup 3+}BO{sub 5} ludwigites and to their complex magnetism and its relationship to relaxor ferroelectricity.
Electric, thermoelectric and magnetic characterization of γ-Fe2O3 and Co3O4 nanoparticles synthesized by facile thermal decomposition of metal-Schiff base complexes
Highlights: • Fe and Co oxide NPs were prepared from Schiff base complexes as new precursors. • The electrical conduction in Fe and Co oxide NPs is governed by hopping processes. • Co{sub 3}O{sub 4} NPs show weak ferromagnetic ordering at room temperature. • γ-Fe{sub 2}O{sub 3} NPs have superparamagnetic behavior. - Abstract: Using novel compounds for synthesis of metal oxide nanomaterials can tune their physical properties due to the associated variation in the shape, size and crystallinity. In this work, γ-Fe{sub 2}O{sub 3} and Co{sub 3}O{sub 4} nanoparticles were successfully prepared by a facile thermal decomposition route, employing [Fe(C{sub 32}H{sub 22}N{sub 4}O{sub 2})]·2H{sub 2}O and [Co(C{sub 16}H{sub 11}N{sub 3}O{sub 4})].(1/2)H{sub 2}O complexes, respectively as new precursors. The x-ray diffraction and high resolution transmission electron microscopy investigation confirmed that the materials consist of highly pure spinel γ-Fe{sub 2}O{sub 3} and Co{sub 3}O{sub 4} nanoparticles with average size of ∼ 9 and 30 nm, respectively. The electrical conduction is governed by the hopping mechanism. The thermoelectric power measurements confirmed that Co{sub 3}O{sub 4} nanoparticles are non-degenerate semiconductor with Fermi energy ∼1.21 eV while γ-Fe{sub 2}O{sub 3} nanoparticles showed a degenerate to non-degenerate transition. The Co{sub 3}O{sub 4} nanoparticles showed a weak ferromagnetic ordering that could be attributed to uncompensated surface spins due to finite-size effects. But γ- Fe{sub 2}O{sub 3} NPs show superparamagnetic behavior at room temperature.
Self-Assembled Magnetic Nanoparticle Layers: Structural Control for Reconfigurable Magnetism and Functional Applications
We advance soft X-ray vector ptychographic tomography to map the 3D magnetization field in self-assembled superparamagnetic nanoparticles at a liquid–liquid interface, revealing how layered structures influence magnetic ordering. We observe that monolayers with low coordination numbers exhibit weak magnetic order, with magnetic vortices disrupting spin alignment. In contrast, bilayers and trilayers with higher coordination numbers display long-range magnetic order with strong spin correlations across larger distances and a suppression of magnetic vortices. We further quantify the average distance for vortex–antivortex pairs as 26.0 ± 2.0 nm, while vortex–vortex and antivortex–antivortex pairs exhibit larger separations, averaging 44.9 ± 5.2 and 54.1 ± 7.4 nm, respectively. These experimental results are supported by micromagnetic Monte Carlo simulations. Our findings illustrate how layered structures enhance magnetic order and spin correlation in superparamagnetic nanoparticle assemblies, providing a promising approach for tuning magnetic properties in applications such as data storage, microrobotics, and biomedicine.
Nanospheres of a New Intermetalic FeSn5 Phase: Synthesis Magnetic Properties and Anode Performance in Li-ion Batteries
We synthesized monodisperse nanospheres of an intermetallic FeSn{sub 5} phase via a nanocrystal-conversion protocol using preformed Sn nanospheres as templates. This tetragonal phase in P4/mcc space group, along with the defect structure Fe{sub 0.74}Sn{sub 5} of our nanospheres, has been resolved by synchrotron X-ray diffraction and Rietveld refinement. Importantly, FeSn{sub 5}, which is not yet established in the Fe-Sn phase diagram, exhibits a quasi-one dimensional crystal structure along the c-axis, thus leading to interesting anisotropic thermal expansion and magnetic properties. Magnetization measurements indicate that nanospheres are superparamagnetic above the blocking temperature T{sub B} = 300 K, which is associated with the higher magnetocrystalline anisotropy constant K = 3.33 kJ m{sup -3}. The combination of the magnetization measurements and first-principles density functional theory calculations reveals the canted antiferromagnetic nature with significant spin fluctuation in lattice a-b plane. The low Fe concentration also leads Fe{sub 0.74}Sn{sub 5} to enhanced capacity as an anode in Li ion batteries.
Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition
Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe 2 O 3 and superparamagnetic Fe 2 O 3 with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe 2 O 3 in a reducing atmosphere leads to the formation of the spinel Fe 3 O 4 phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. Finally, the ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.
Evidence of Magnetic Inversion in Single Ni Nanoparticles
Superparamagnetism is an unwanted property of small magnetic particles where the magnetization of the particle flips randomly in time, due to thermal noise. There has been an increased attention in the properties of superparamagnetic particles recently, because of their potential applications in high density storage and medicine. In electron transport through single nanometer scale magnetic particles, the current can also cause the magnetization to flip randomly in time, even at low temperature. Here we show experimental evidence that when the current is then reduced towards zero in the applied magnetic field, the magnetization can reliably freeze about a higher anisotropy-energy minimum, where it tends to be inverted with respect to the magnetic field direction. Specifically, we use spin-unpolarized tunneling spectroscopy of discrete levels in single Ni particles 2–4 nm in diameter at mK-temperature, and find that the the magnetic excitation energy at the onset of current decreases when the magnetic field increases, reaching near degeneracy at nonzero magnetic field. We discuss the potential for spintronic applications such as current induced magnetization switching without any spin-polarized leads.
Electronic structure of cobalt doped CdSe quantum dots using soft X-ray spectroscopy
Here, the electronic structure and magnetic properties of cobalt doped CdSe quantum dots (QDs) are studied using electron microscopy, soft X-ray spectroscopy, and magnetometry. Magnetometry measurements suggest these QDs are superparamagnetic, contrary to a spin-glass state observed in the bulk analogue. Electron microscopy shows well formed QDs, but with cobalt existing as doped into the QD and as unreacted species not contained in the QD. X-ray absorption measurements at the Co L3-edge suggest that changes in spectra features as a function of particle size can be described considering combination of a cobalt ion in a tetrahedral crystal field and an octahedrally coordinated (impurity) phase. With decreasing particle sizes, the impurity phase increases, suggesting that small QDs can be difficult to dope.
Magnetic gold nanotriangles by microwave-assisted polyol synthesis
Simple approaches to synthesize hybrid nanoparticles with magnetic and plasmonic functionalities, with high control of their shape and avoiding cytotoxic reactants, to target biomedical applications remain a huge challenge. Here, we report a facile, fast and bio-friendly microwave-assisted polyol route for the synthesis of a complex multi-material consisting of monodisperse gold nanotriangles around 280 nm in size uniformly decorated by superparamagnetic iron oxide nanoparticles of 5 nm. These nanotriangles are readily dispersible in water, display a strong magnetic response (10 wt% magnetic fraction) and exhibit a localized surface plasmon resonance band in the NIR region (800 nm). Moreover, these hybrid particles can be easily self-assembled at the liquid–air interfaces.
Rapid microwave-assisted synthesis of dextran-coated iron oxide nanoparticles for magnetic resonance imaging
Currently, magnetic iron oxide nanoparticles are the only nanosized magnetic resonance imaging (MRI) contrast agents approved for clinical use, yet commercial manufacturing of these agents has been limited or discontinued. Though there is still widespread demand for these particles both for clinical use and research, they are difficult to obtain commercially, and complicated syntheses make in-house preparation unfeasible for most biological research labs or clinics. To make commercial production viable and increase accessibility of these products, it is crucial to develop simple, rapid and reproducible preparations of biocompatible iron oxide nanoparticles. Here, we report a rapid, straightforward microwave-assisted synthesis of superparamagnetic dextran-coated iron oxide nanoparticles. The nanoparticles were produced in two hydrodynamic sizes with differing core morphologies by varying the synthetic method as either a two-step or single-step process. A striking benefit of these methods is the ability to obtain swift and consistent results without the necessity for air-, pH- or temperature-sensitive techniques; therefore, reaction times and complex manufacturing processes are greatly reduced as compared to conventional synthetic methods. This is a great benefit for cost-effective translation to commercial production. The nanoparticles are found to be superparamagnetic and exhibit properties consistent for use in MRI. In addition, the dextran coating imparts the water solubility and biocompatibility necessary for in vivo utilization.
Dynamic magnetic permeability of the heterogeneous nanosystems based on (Co{sub 41}Fe{sub 39}B{sub 20}){sub x}(SiO{sub 2}){sub 100–} {sub x} composites
Thin films of (Co{sub 41}Fe{sub 39}B{sub 20}){sub x}(SiO{sub 2}){sub 100–} {sub x} nanocomposites and hybrid nanocomposite–semiconductor [(Co{sub 41}Fe{sub 39}B{sub 20}){sub x}(SiO{sub 2}){sub 100–} {sub x}/C]{sub 50} multilayers are synthesized by ion-beam deposition at various contents x of ferromagnetic metallic Co{sub 41}Fe{sub 39}B{sub 2O} nanogranules in an SiO{sub 2} matrix and at various carbon layer thicknesses h < 2 nm. Their magnetic and electrical properties, high-frequency magnetic permeability, magnetooptical spectra, and FMR spectra are studied. It is found that both the single-layer nanocomposites and the multilayers with carbon interlayers are superparamagnetic at x < x{sub per}, where x{sub per} is the electric conduction percolation threshold: a hysteresis at room temperature is absent, and the blocking temperature determined in quasi-static measurements does not exceed 20–30 K and weakly depends on the carbon layer thickness. At a carbon layer thickness h = 1.2–1.8 nm, the real and imaginary parts of complex magnetic permeability at 50 MHz and room temperature are substantially higher than those of the nanocomposites without carbon layers: their values are typical of ferromagnets. This dependence points to an exchange interaction between nanogranules in layers through a carbon interlayer. The influence of a conducting layer on the static and dynamic magnetic properties of a system of interacting superparamagnetic particles is discussed.
Influence of carbon chain length on the synthesis and yield of fatty amine-coated iron-platinum nanoparticles
Iron oxide nanoparticles are among the most widely used and characterized magnetic nanoparticles. However, metal alloys such as superparamagnetic iron-platinum particles (SIPPs), which have better magnetic properties, are receiving increased attention. Scalable techniques to routinely synthesize SIPPs in bulk need further study. Here, we focus on the role played by the fatty amine ligand in the formation of the bimetallic FePt nanocrystal. More specifically, we compare the effect of varying lengths of fatty amine ligands on the shape, structure, uniformity, composition, and magnetic properties of the SIPPs. We synthesized SIPPs by employing a ‘green’ thermal decomposition reaction using fatty amine ligands containing 12 to 18 carbons in length. Greater fatty amine chain length increased the polydispersity, particle concentration, iron concentration, and the stability of the SIPPs. Additionally, longer reflux times increased the diameter of the particles, but decreased the iron concentration, suggesting that shorter reaction times are preferable. Fourier transform infrared spectroscopy of the SIPPs indicates that the ligands are successfully bound to the FePt cores through the amine group. Superconducting quantum interference device magnetometry measurements suggest that all of the SIPPs were superparamagnetic at room temperature and that SIPPs synthesized using tetradecylamine had the highest saturation magnetization. Our findings indicate that the octadecylamine ligand, which is currently used for the routine synthesis of SIPPs, may not be optimal. Overall, we found that using tetradecylamine and a 30-min reflux reaction resulted in optimal particles with the highest degree of monodispersity, iron content, stability, and saturation magnetization.
Active Experiments in Space: The Future
Planned active space experiments and ideas for future active space experiments are reviewed. Three active experiments being readied are DSX (Demonstration and Space eXperiments), SMART (Space Measurement of Rocket-released Turbulence), and BeamPIE (Beam Plasma Interaction Experiment). Ideas for future experiments include relativistic-electron-beam experiments for magnetic-field-line tracing, relativistic-electron-beam experiments to probe the middle atmosphere, plasma-wave launching using superparamagnetic-nanoparticle amplification of magnetic fields, the heavy-ion mass loading of collisionless magnetic-field-line reconnection, the use of electrostatically charged tethers to pitch-angle scatter radiation-belt particles, cold plasma releases to modify magnetospheric plasma physics, and neutral-gas releases to enhance neutral-particle imaging of the magnetosphere. Technologies that are being developed to enable future space active experiments are reviewed: this includes the development of compact relativistic accelerators, superparamagnetic particle amplified antennae, CubeSats, and a new understanding of how to control dynamic spacecraft charging. New capabilities to use laboratory facilities to design space active experiments as well as new computer-simulation capabilities to design and understand space active experiments are reviewed.
Functionalized magnetic nanoparticle analyte sensor
A method and system for simply and efficiently determining quantities of a preselected material in a particular solution by the placement of at least one superparamagnetic nanoparticle having a specified functionalized organic material connected thereto into a particular sample solution, wherein preselected analytes attach to the functionalized organic groups, these superparamagnetic nanoparticles are then collected at a collection site and analyzed for the presence of a particular analyte.
Green Synthesis of Fe{sub 3}O{sub 4}/Cellulose/Polyvinyl Alcohol Hybride Aerogel and Its Application for Dye Removal
A novel Fe{sub 3}O{sub 4}/cellulose–polyvinyl alcohol (PVA) aerogel was successfully synthesized by an eco-friendly and facile method in this work. Cellulose/PVA matrix was prepared through an environmental friendly physical cross-linking process and further in-situ decorated with Fe{sub 3}O{sub 4}. Series of Fe{sub 3}O{sub 4} decorated aerogels were prepared and the effects of Fe{sub 3}O{sub 4} nanoparticles (NPs) on the aerogels were systematic investigated. As-prepared aerogels exhibited desirable properties including nanostructure, relatively high porosity, improved mechanical and superparamagnetism. The TEM results showed that Fe{sub 3}O{sub 4} NPs were integrated in the three-dimensional matrix of cellulose/PVA with a diameter of 9–12 nm. Furthermore, the mechanical strength of the aerogels was significantly enhanced after the introduction of Fe{sub 3}O{sub 4} NPs. Meanwhile, the obtained Fe{sub 3}O{sub 4}/cellulose/PVA aerogel exhibited excellent adsorption performance toward methyl blue dye, and can be reused through fenton-like catalysts oxidative degradation of organic dye in H{sub 2}O{sub 2} solution. Therefore, they will have a great potential application as eco-friendly and economical adsorbents.
Luteolin-Loaded Spion as a Drug Carrier for Cancer Cell In Vitro
The aim of this study is to determine the cytotoxic and apoptotic effects of newly synthesized folic acid (FA) and luteolin (carboxylated luteolin (CL)) conjugated superparamagnetic nanoparticle (SPION@FA-PEG@CL) on folate receptor positive (FAR (+)) and negative (FAR (−)) cell lines in vitro. Cytotoxicity analysis by real-time cell analyzer system (RTCA) and apoptosis by TUNEL and Annexin assay, Caspase 3/7 activities, and Caspase 3/7 expression level were determined. According to RTCA results, SPION@FA-PEG@CL nanodrug showed higher cytotoxicity against U87, MCF-7, HeLa cell lines in comparison with L929 and A549 cell lines. TUNEL and Annexin assays indicated that SPION@FA-PEG@CL increased the apoptotic and necrotic cell ratio in FAR (+) cell. In L929 and A549 cells, are FAR (−) cell lines apoptotic and necrotic cell ratio was lower than FAR (+) cell lines (U87, MCF-7 and HeLa). Caspase 3 and 7 analyses also showed that SPION@FA-PEG@CL nanodrug have apoptotic and necrotic impact on cell lines, they were higher in FAR (+) cells than FAR (−) cells. According to results, synthesized SPION@FA-PEG@CL can be a novel nanodrug delivery system for in cancer chemotherapy.