Search

Superparamagnetic iron oxide nanoparticles (SPIONs) are nanoparticles used in a lot of applications such as batteries, and biomedical, ... To obtain these nanoparticles, several techniques exist such as coprecipitation, thermal decomposition, sol–gel process but they have some advantages (synthesis in a water media, high crystallinity, high monodispersity) and disadvantages (using an organic solvent, large distribution of size, poor crystallinity). The goal of this work is to synthesize SPIONs for biomedical applications (for example as a contrast agent for the MRI): SPIONs should be stable in an aqueous media, monodisperse, and have good crystallinity and magnetic properties. To achieve this result, a microwave process is carried out. However, any study describes the microwave parameter on the synthesis of the nanoparticles. This work offers to determine the best conditions of the microwave to obtain ideal SPIONs for MRI. For this, an experimental design is carried out to determine these parameters thanks to different techniques of characterization (Transmission Electronic Microscopy, Dynamic Light Scattering, X‐ray diffraction, Thermogravimetric Analysis, magnetic characterizations). With the different results of these characterizations, the best conditions of the microwave are determined, and a simulation of all experiments is realized with a surface response. [ABSTRACT FROM AUTHOR]

We used magnetic and synchrotron X-ray diffraction measurements to investigate the possibility of tuning the strength of magnetic interparticle interactions in nanoparticle ensembles via chemical manipulation. Our main result comes from temperature-resolved in-phase ac-susceptibility data collected on 8 nm average-diameter Ni0.25Zn0.75Fe2O4 (Ni25) and Ni0.5Zn0.5Fe2O4 (Ni50) nanoparticles at different frequencies, χ′ vs. T|f. We found that the relative peak temperature variation per frequency decade, ϕ = ∆ T T · ∆ l o g (f) —a known measure of interparticle interaction strength—exhibits a four-fold increase, from ϕ = 0.04 in Ni50 to ϕ = 0.16 in Ni25. This corresponds to a fundamental change in the nanoparticles' superspin dynamics, as proven by the fit of phenomenological models to magnetic relaxation data. Indeed, the Ni25 ensemble exhibits superparamagnetic behavior, where the temperature dependence of the superspin relaxation time, τ, is described in the Dorman–Bessais–Fiorani (DBF) model: τ T = τ r exp ⁡ E B + E a d k B T ,   with parameters τr = 4 × 10−12 s, and (EB + Ead)/kB = 1473 K. On the other hand, the nanoparticles in the Ni50 ensemble freeze collectively upon cooling in a spin-glass fashion according to a critical dynamics law: τ (T) = τ 0 T T g − 1 z ν , with τ0 = 4 × 10−8 s, Tg = 145 K, and zν = 7.2. Rietveld refinements against powder X-ray diffraction data reveal the structural details that underlie the observed magnetic behavior: an indirect cation replacement mechanism by which non-magnetic Zn ions are incorporated in the tetrahedral sites of the inverse spinel. [ABSTRACT FROM AUTHOR]

Abstract Acoustic metamaterials are growing in popularity for sound applications including noise control. Despite this, there remain significant challenges associated with the fabrication of these materials for the sub-100 Hz regime, because acoustic metamaterials for such frequencies typically require sub-mm scale features to control sound waves. Advances in additive manufacturing technologies have provided practical methods for rapid fabrication of acoustic metamaterials. However, there is a relatively high sensitivity of their resonant characteristics to sub-mm deviations in geometry, pushing the limits of additive manufacturing. One way of overcoming this is via active control of device resonance. Here, an acoustic metamaterial cell with adjustable resonance is demonstrated for the sub-100 Hz regime. A functionally superparamagnetic membrane—devised to facilitate the fabrication process by eliminating magnetic poling requirements—is engineered using stereolithography, and its mechanical and acoustic properties are experimentally measured using laser Doppler vibrometry and electret microphone testing, with a mathematical model developed to predict the cell response. It is demonstrated that an adjustable magnetic acoustic metamaterial can be fabricated at ultra-subwavelength dimensions ( $$\le \lambda$$ ≤ λ /77.5), exhibiting adjustable resonance from 88.73 to 86.63 Hz. It is anticipated that this research will drive new innovations in adjustable metamaterials, including wider frequency ranges.

In this study, computational techniques based on artificial neural networks for three models were used for training sets, Néel's relaxation time, particle Length and the decay of magnetization were used to perform superparamagnetic calculations for Co3Pt and FePt typical magnetic storage medium. The magnetic medium's magnetisation stability was studied using the thermal stability coefficient by determining the Néel relaxation time. The superparamagnetic limit was discovered to determine the size of the magnetic particle that can maintain its magnetization for over 10 years, larger particles (8 nm3 for FePt and 64 nm3 for Co3Pt) are required. The decay of magnetization occurs when the thermal stability factor exceeds 40. the effect of changing the neural network's parameters on its performance was examined. The results demonstrated the high sensitivity of the designed neural network's response, which relies on the backpropagation technique to change these parameters. [ABSTRACT FROM AUTHOR]

The development of nanoribbon-like structures is an effective strategy to harness the potential benefits of graphenic materials due to their excellent electrical properties, advantageous edge sites, rapid electron transport, and large specific area. Herein, parallel and connected magnetic nanostructured nanoribbons are obtained through the synthesis of reduced graphene oxide (rGO) using NiCl2 as a precursor with potential applications in nascent electronic and magnetic devices. Several analytical techniques have been used for the thorough characterization of the modified surfaces. Atomic force microscopy (AFM) shows the characteristic topographical features of the nanoribbons. While X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy provided information on the chemical state of Ni and graphene-like structures, magnetic force microscopy (MFM) and scanning Kelvin probe microscopy (SKPFM) confirmed the preferential concentration of Ni onto rGO nanoribbons. These results indicate that the synthesized material shows 1D ordering of nickel nanoparticles (NiNPs)-decorating tiny rGO flakes into thin threads and the subsequent 2D arrangement of the latter into parallel ribbons following the topography of the HOPG basal plane. [ABSTRACT FROM AUTHOR]

The electron–electron, or zero-field interaction (ZFI) in the electron paramagnetic resonance (EPR) of high-spin transition ions in metalloproteins and coordination complexes, is commonly described by a simple spin Hamiltonian that is second-order in the spin S: H = D [ S z 2 − S S + 1 / 3 + E (S x 2 − S y 2) . Symmetry considerations, however, allow for fourth-order terms when S ≥ 2. In metalloprotein EPR studies, these terms have rarely been explored. Metal ions can cluster via non-metal bridges, as, for example, in iron-sulfur clusters, in which exchange interaction can result in higher system spin, and this would allow for sixth- and higher-order ZFI terms. For metalloproteins, these have thus far been completely ignored. Single-molecule magnets (SMMs) are multi-metal ion high spin complexes, in which the ZFI usually has a negative sign, thus affording a ground state level pair with maximal spin quantum number mS = ±S, giving rise to unusual magnetic properties at low temperatures. The description of EPR from SMMs is commonly cast in terms of the 'giant-spin model', which assumes a magnetically isolated system spin, and in which fourth-order, and recently, even sixth-order ZFI terms have been found to be required. A special version of the giant-spin model, adopted for scaling-up to system spins of order S ≈ 103–104, has been applied to the ubiquitous iron-storage protein ferritin, which has an internal core containing Fe3+ ions whose individual high spins couple in a way to create a superparamagnet at ambient temperature with very high system spin reminiscent to that of ferromagnetic nanoparticles. This scaled giant-spin model is critically evaluated; limitations and future possibilities are explicitly formulated. [ABSTRACT FROM AUTHOR]

This study aimed to develop multifunctional nanoplatforms for both cancer imaging and therapy using superparamagnetic iron oxide nanoparticles (SPIONs). Two distinct synthetic methods, reduction–precipitation (MR/P) and co-precipitation at controlled pH (MpH), were explored, including the assessment of the coating's influence, namely dextran and gold, on their magnetic properties. These SPIONs were further functionalized with gadolinium to act as dual T1/T2 contrast agents for magnetic resonance imaging (MRI). Parameters such as size, stability, morphology, and magnetic behavior were evaluated by a detailed characterization analysis. To assess their efficacy in imaging and therapy, relaxivity and hyperthermia experiments were performed, respectively. The results revealed that both synthetic methods lead to SPIONs with similar average size, 9 nm. Mössbauer spectroscopy indicated that samples obtained from MR/P consist of approximately 11–13% of Fe present in magnetite, while samples obtained from MpH have higher contents of 33–45%. Despite coating and functionalization, all samples exhibited superparamagnetic behavior at room temperature. Hyperthermia experiments showed increased SAR values with higher magnetic field intensity and frequency. Moreover, the relaxivity studies suggested potential dual T1/T2 contrast agent capabilities for the coated SPpH-Dx-Au-Gd sample, thus demonstrating its potential in cancer diagnosis. [ABSTRACT FROM AUTHOR]

The effect of swift heavy ion irradiation on sol–gel-prepared maghemite nanoparticles was studied by 57Fe transmission Mössbauer spectroscopy and X-ray diffractometry (XRD). The room temperature Mössbauer spectra of the non-irradiated nano-maghemite showed poorly resolved magnetically split, typical relaxation spectra due to the superparamagnetic state of the nanoparticles. Significant changes in the line shape, indicating changes in the superparamagnetic state, were found in the Mössbauer spectra upon irradiation by 160 MeV and 155 MeV 132Xe26+ ions with fluences of 5 × 1013 ion cm−2 and 1 × 1014 ion cm−2. XRD of the irradiated maghemite nanoparticles showed a significant broadening of the corresponding lines, indicating a decrease in the crystallite size, compared to those of the non-irradiated ones. The results are discussed in terms of the defects induced by irradiation and the corresponding changes related to the change in particle size and consequently in the superparamagnetic state caused by irradiation. [ABSTRACT FROM AUTHOR]

The paper examines the impact of interparticle interactions on the superparamagnetic relaxation of ultrasmall nanoparticle ensembles, using Fe2O3∙nH2O iron oxyhydroxide (ferrihydrite) nanoparticles as an example. Two samples were analyzed: ferrihydrite of biogenic origin (with an average particle size of ≈ 2.7 nm) with a natural organic shell, and a sample (with ≈ 3.5 nm) that underwent low-temperature annealing, during which the organic shell was partially removed. The DC and AC magnetic susceptibilities (χ′(T), χ′′(T)) in a small magnetic field in the superparamagnetic (SPM) blocking region of the nanoparticles were measured. The results show that an increase in interparticle interactions leads to an increase in the SPM blocking temperature from 28 to 52 K according to DC magnetization data. It is shown that below the SPM blocking temperature, magnetic interactions of nanoparticles lead to the formation of a collective state similar to spin glass in bulk materials. The scaling approach reveals that the dynamics of correlated magnetic moments on the particle surface slow down with increasing interparticle interactions. Simulation of χ′′(T) dependence has shown that the dissipation of magnetic energy occurs in two stages. The first stage is directly related to the blocking of the magnetic moment of nanoparticles, while the second stage reflects the spin-glass behavior of surface spins and strongly depends on the strength of interparticle interactions. [ABSTRACT FROM AUTHOR]

The mineral composition, petrographic structure, and magnetic properties of artificial glasses obtained from high-temperature melting of mixtures of rocks of various geneses (volcanic–sedimentary rocks, quartzite–shales, and psammite–silt–pelite complexes) are studied. When glasses were synthesized, cooling and glass transition conditions of various durations were used. The formation of ferrimagnetic minerals is due to the composition of the stock and the cooling rate of the melt. The resulting magnetic particles during "fast" cooling are mainly in the superparamagnetic state (up to 90% or more of the total amount of the magnetic phase in a sample). A mixture of particles of different sizes is formed during "slow" cooling and, as a result, in different magnetic states: from superparamagnetic to the low-domain state. The ferrimagnetic phase that crystallizes in artificial glasses is as chemically heterogeneous iron oxide aggregates, mainly non-stoichiometric magnetite. [ABSTRACT FROM AUTHOR]

This study presents the effect of chitosan on the properties of zinc ferrite nanoparticles suitable for potential biomedical applications. The co‐precipitation method is employed to fabricate these bio‐composites that exhibit excellent microstructural properties. The X‐ray diffractometer (XRD) analysis confirms the presence of a cubic spinel structure in the zinc ferrite‐chitosan bio‐composites, indicative of their crystalline nature. Scanning electron microscope (SEM) imaging revealed spherical particles with a size distribution below 100 nm, demonstrating the successful synthesis of homogenous nanosized particles. Fourier transform infrared spectroscopy (FTIR) spectroscopy analysis identifies the active functional groups within the bio‐composites, providing valuable insights into the molecular structure and interactions present in the synthesized materials. The presence of chitosan is confirmed, highlighting its role in modifying the chemical composition and enhancing the biocompatibility of the samples. UV–vis absorption spectra analysis reveals that the samples exhibits absorbance within the visible range. Vibrating sample magnetometer (VSM) analysis demonstrates the superparamagnetic behavior of the samples. Remarkably, these formulated samples exhibit superparamagnetism with zero coercivity and a magnetization of ≈0.0125 emu g−1 at 5 kOe when doped with chitosan. These properties are crucial for potential biomedical applications making it a promising candidate for various biomedical applications. [ABSTRACT FROM AUTHOR]

LaFeO3 perovskite oxide were synthesized through solution combustion technique using ascorbic acid as phytochemical fuel. The sample was characterized using techniques such as XRD, FTIR, UV-Visible spectroscopy, SEM with EDX and XPS. The magnetic hysteresis behavior was studied using VSM measurement at room temperature. The orthorhombic primitive lattices of LaFeO3 under the space group Pnma was confirmed from XRD pattern and the lattice parameters were obtained using Rietveld profile refinement. The crystallographic structure and lattice parameters were found consistent with the data presented in the ICDD PCPDFWIN Number 37-1493 file. Using Scherrer equation the average crystallite size (26 nm) was estimated. The strain separated effective crystallite size (35 nm) was estimated using the model suggested by Williamson–Hall. The M–O bond vibration bands correspond to LaFeO3 crystal lattice were elucidated from FTIR spectrum. Using the raw reflectance data from UV-Visible spectrum, Tauc' plot analysis employing Kubelka Munk function was performed; from which the optical direct band gap (2.41 eV) was estimated. The particle size distribution and elemental composition were estimated from SEM with EDX. The binding energies obtained from deconvoluted XPS spectra accurately provide the valence state electronic configuration corresponding to La and Fe atoms in the prepared LaFeO3 sample. The weak ferromagnetic relaxation with finite coercivity (0.18248 kOe) and remanent magnetization (0.2825 emu. g−1) was estimated from M–H curve analysis using VSM data at room temperature. [ABSTRACT FROM AUTHOR]

Present work reports a systematic study on the evaluation of magnetic inhomogeneities in non-stoichiometric Mg 0·5 Ca 0·5 Fe 2 O 4 nanoferrite (MCNF) by conducting exhaustive dc-magnetization, ac-susceptibility and 57Fe Mössbauer spectroscopic measurements and exchange bias investigations using training protocol down to 6 K. Rietveld fitting to PXRD established the formation of anticipated spinel fcc phase of MCNF (non-stoichiometric) along with a minute impurity phase of calcite. Scherrer method and HRTEM micrographs illustrated broad size distribution of MCNF nanoparticles with an average nanocrystallite size of ∼15 nm. Combined 57Fe Mössbauer spectroscopic and dc-magnetization analysis establishes coexistence of ferrimagnetic (67 %) & superparamagnetic (33 %) states at 300 K with notable M s = 22 emu/g, M r = 4 emu/g & H c = 130 Oe and blocking of most of the nanoparticles of MCNF below 300 K. The coercivity followed the size-modified Kneller law for ferrimagnetic nanoparticles and the saturation magnetization abides the Bloch law. Moreover the frequency-dependent ac-susceptibility investigations revealed two magnetic transitions: (i) A transition at ∼ 330 K in the low frequency data attributed to the relaxation of blocked particles of bigger sizes under the superparamagnetic (SPM) regime and (ii) an irregularity at low temperatures is assigned to surface spin glass freezing. Surface spin glass freezing was further affirmed by the ageing experiments and dynamic scaling law. Furthermore, even the best fit to the dynamic scaling couldn't assert the existence of conventional spin glass phase due to slower spin-flip time of surface spins. A soft ferrimagnetic core of MCNF is enveloped with disordered surface spins, which manifest spin glass state. Concurrently, the findings of exchange bias at 30 K and training effect at 6 K affirmed that MCNF nanoparticles are presenting themselves as FM core- SG shell system. Our experimental findings suggested magnetic inhomogeneities comprised of superparamagnetism, ferrimagnetism and disordered surface spin glass state in the non-stoichiometric MCNF. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive analysis of the magnetic properties of pristine and citric acid-coated cobalt ferrite (${\rm{CoF}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{4}}}$ CoF e 2 O 4 ) nanoparticles (NPs) dispersed in the host nematic $4{^{\prime}}$ 4 ′ -heptyl-4-biphenylcarbonnitrile (7CB) system. Our results shed light on the promising potential of combining liquid crystals (LC) with magnetic nanoparticles for cancer treatment. This opens up exciting avenues for further exploration and possible applications in the field of oncology. The study focuses on examining the magnetic behaviour of LC dispersed systems with two concentrations of magnetic nanoparticles (0.03 and 0.04 wt%). Notably, intriguing temperature-dependent magnetisation plots reveal a distinctive cusp, which can be attributed to the freezing phenomenon of the liquid crystal. This observation offers valuable insights into the system's magnetic properties and interactions, deepening our understanding of its behavior. [ABSTRACT FROM AUTHOR]

In this work, an eco-friendly “green” nanocomposite of chitosan containing graphite and maghemite (g-Fe2O3) nanoparticles were prepared by solution casting method. The effect of g-Fe2O3 nanoparticles on structural, electric and dielectric properties of Chitosan-graphite (Cs-graphite) composites was investigated. The dielectric constant of Cs-graphite composites increased with incorporation of g-Fe2O3 nanoparticles. Among the composites Cs-20% graphite - 20% g-Fe2O3 has dielectric constant of ~16.5 at 1 MHz at room temperature. With increase in temperature the dielectric constant varied significantly. The conductivity of Cs-graphite is enhanced by one order of magnitude with addition of g-Fe2O3 nanoparticles, and the value is found to be 5.7x10-6 S/cm. Various parameters such as dielectric constant, dielectric loss, electric modulus, conductivity, activation energy were analyzed. Magnetic measurement of g-Fe2O3 nanoparticles and the PNCs showed superparamagnetic behaviour. A model is proposed to explain the observed dielectric behavior of polymer nanocomposites (PNCs). The formation of microcapacitors by incorporation of maghemite nanoparticles between graphite is proposed.

Present work focuses to investigate the impact of rare earth ions (Ce and Gd) on the structural and magnetic properties of nanocrystalline nickel-zinc ferrite. The nanoparticles of Ni0.5Zn0.5Fe2O4, Ni0.5Zn0.5Ce0.02Fe1.98O4, and Ni0.5Zn0.5Gd0.02Fe1.98O4 were synthesized by citric acid–assisted sol–gel method. The formation of cubic spinel structure without additional impurity peaks was confirmed by X-ray diffraction (XRD) pattern. The crystallite size of Ni0.5Zn0.5Fe2O4 (R = 0) and Ni0.5Zn0.5R0.02Fe1.98O4 (R = Ce and Gd) nanoparticles was observed less than ~ 35 nm at sintering temperatures of ~ 300 to ~ 500 ℃. From magnetic measurements, the value of room temperature saturation magnetization of superparamagnetic Ni0.5Zn0.5Fe2O4 (R = 0) was found to be reduced with the doping of Ce and Gd ions from 44.19 ± 0.02 to 39.33 ± 0.03 emu/g and 35.18 ± 0.02 emu/g, respectively, at 300 ℃ and from 60.69 ± 0.04 to 54.11 ± 0.03 emu/g and 55.72 ± 0.04 emu/g, respectively, at 500 ℃. The detailed study of superparamagnetic relaxation in pure and rare earth-doped samples was performed by the thermal magnetization measurements under zero field cool (ZFC) and field cool (FC) processes. Mossbauer spectra revealed the absence of the quadrupole splitting for Ni0.5Zn0.5Ce0.02Fe1.98O4 at tetrahedral (A-site) and octahedral (B-site) sites which indicated cubic symmetry in the crystal structure. Although, the presence of negative asymmetry was observed in Ni0.5Zn0.5Gd0.02Fe1.98O4-doped ferrite sample. Magnetic materials with superparamagnetic properties are desirable in various biomedical applications. [ABSTRACT FROM AUTHOR]

Magnetite nanoparticles have attracted interest of researchers from different science fields such as medicine, biology, physics, or chemistry due to their multifunctional properties including biocompatibility, superparamagnetism and low toxicity. Several methods have been developed to synthesize magnetic nanoparticles with controlled size, shape, and magnetic properties. Among them, coprecipitation is the most widely used because of several advantages such as high-yield production of nanoparticles, its simplicity, low-cost and its eco-friendly reaction conditions, but it also has low reproducibility. To achieve the magnetic nanoparticles with the desired properties, the investigation and control of reaction parameters are essential. In this article, the mechanism of coprecipitation reaction for magnetite nanoparticle synthesis and recent studies in reaction parameters controlling the particle properties will be reviewed. In addition, the most used methods for structural and magnetic characterization of magnetite and magnetite functionalized nanoparticles are presented and exemplified. [ABSTRACT FROM AUTHOR]

Gold nanoclusters (AuNCs) with fluorescence in the Near Infrared (NIR) by both one- and two-photon electronic excitation were incorporated in mesoporous silica nanoparticles (MSNs) using a novel one-pot synthesis procedure where the condensation polymerization of alkoxysilane monomers in the presence of the AuNCs and a surfactant produced hybrid MSNs of 49 nm diameter. This method was further developed to prepare 30 nm diameter nanocomposite particles with simultaneous NIR fluorescence and superparamagnetic properties, with a core composed of superparamagnetic manganese (II) ferrite nanoparticles (MnFe2O4) coated with a thin silica layer, and a shell of mesoporous silica decorated with AuNCs. The nanocomposite particles feature NIR-photoluminescence with 0.6% quantum yield and large Stokes shift (290 nm), and superparamagnetic response at 300 K, with a saturation magnetization of 13.4 emu g−1. The conjugation of NIR photoluminescence and superparamagnetic properties in the biocompatible nanocomposite has high potential for application in multimodal bioimaging. [ABSTRACT FROM AUTHOR]

Highly dispersed Ni‐TiO2 catalyst has been studied in the process of preparation and under catalytic transfer hydrogenation reaction conditions in supercritical 2‐propanol (250°C, 70 bar) using electron spin resonance in situ. Electron spin resonance in situ has been used to study the process of the catalyst passivation and subsequent reduction of the oxide layer in the gas flow. Reduction of the NiO layer on the surface of passivated Ni nanoparticles has been detected in supercritical 2‐propanol, which is in agreement with kinetic modeling data. It has been found that the reduction of the nickel oxide layer in supercritical 2‐propanol occurs at a lower temperature compared with the reduction in hydrogen flow, according to in situ electron spin resonance study. [ABSTRACT FROM AUTHOR]

Nanocarriers of anticancer drugs are delicately designed with precision addition at every attempt. In this paper, we report CuCo2S4 nanoparticles that show light absorption in the near infrared-II wavelength range and possess magnetic characteristics. The synthesized nanoparticles are characterized by X-ray diffraction, Scanning Electron Microscopy, Dynamic Light Scattering, Thermogravimetry, and X-ray Photoelectron spectroscopy methods. The nanoparticles form a composite with biocompatible polymeric β-cyclodextrin. The nanoparticles possess a band gap energy of 2.25 eV. The magnetic property arises due to the cobalt incorporation in the nanoparticles. The anticancer drug camptothecin is loaded in the nanocarrier with an 89% adsorption efficiency. The in vitro release of the drug occurs in a sustained fashion. Further, the in vitro anticancer potential of the nanocarrier is examined on breast cancer (MDA-MB-231) cell lines, and the activities of the free- and the drug-loaded nanocarrier is compared. The cobalt-containing copper sulfide nanoparticle-poly-β-cyclodextrin composite works as a promising nanocarrier of camptothecin. [ABSTRACT FROM AUTHOR]

A series of La3+ ion doped magnesium nickel ferrites, Mg 0.5 Ni 0.5 Fe 2-x La x O 4 (0 ≤ x ≤ 0.1) having a cubic spinel structure were prepared by the co-precipitation method. Various characterization techniques, including X-ray diffractometer (XRD), high resolution transmission electron microscopy (HR-TEM), electron spin resonance (ESR) and vibrating sample magnetometer (VSM) were used to investigate structural and magnetic properties. The average crystallite size decreases and lattice parameter increases with La3+ ion doping and lie in the range of 12–7 nm and 8.347–8.361 Å respectively. Analysis of ESR spectra reveals that, g-value with La3+ ion addition decreases from 2.57 to 2.12. The saturation magnetization and the coercivity decrease with increasing rare-earth content. Magnetic-hysteresis (M − H) loop shifts from a ferromagnetic to a superparamagnetic nature with La3+ ion addition. The dielectric study was carried out in the frequency range of 1 KHz to 4000 KHz and temperature ranging 30 °C–350 °C using the impedance analyzer. The dielectric constant decreases with increasing frequency and the La3+ ion concentration. The dielectric loss of the sample increases with increasing temperature. The magnetic properties of the synthesized nanoparticles make them a potential material for stable ferrofluid application and the low tangent loss value makes these material a potential candidate for frequency-based applications. [ABSTRACT FROM AUTHOR]

Ni0.5Zn0.5Fe2O4 ferrite nanoparticles were synthesized by high-energy ball-milling using binary oxide precursors, followed by a subsequent heat treatment at comparatively lower temperature (500 °C for 1 h) to promote the redistribution of the cations to their equilibrium positions. Although, several articles are available on Ni–Zn ferrite nanoparticles, the magnetic data of ball-milled sample has hardly been analysed based on existing theoretical models to extract useful information. The samples were characterized by X-ray diffraction, scanning electron microscopy and dc magnetization study. The average crystallite sizes estimated from the structural data (using Scherrer equation) are found to be around 14.4 nm. The temperature and field variation of magnetic data suggests a superparamagnetic nature with a distribution of particle sizes. The zero field cooled and field cooled magnetization data are analysed based on a theoretical model of superparamagnetic particles with a log-normal distribution, resulting in an average particle size of 24.4 nm (width parameter of 0.23). The Langevin function adequately describes the field variation of magnetization (M–H) data at room temperature, in addition to a paramagnetic contribution, suggesting the existence of significant spin disorder. The above fit yields an average magnetic moment of 7860 μ B . The results of the magnetic study corroborate well with the structural and morphological characteristics. [ABSTRACT FROM AUTHOR]

Artificial glasses containing nanoscale inclusions of iron oxides, including magnetite and hematite, were obtained via the method of the high-temperature melting of rocks. The main factors influencing the magnetic properties of glasses are the composition of the initial charge and the conditions of cooling of the melt. The data of magnetic granulometry and frequency-field dependencies of magnetic susceptibility showed the presence of a sufficiently large superparamagnetic fraction in the samples. Coordinated theoretical modeling using two independent models that take into consideration possible the chemical inhomogeneity of particles and magnetostatic interaction between them made it possible to calculate hysteresis characteristics corresponding to the experiment and to estimate ferrimagnetic concentrations in the samples, including the superparamagnetic fraction. [ABSTRACT FROM AUTHOR]

We used magnetic and synchrotron X-ray diffraction measurements to investigate the possibility of tuning the strength of magnetic interparticle interactions in nanoparticle ensembles via chemical manipulation. Our main result comes from temperature-resolved in-phase ac-susceptibility data collected on 8 nm average-diameter Ni0.25Zn0.75Fe2O4 (Ni25) and Ni0.5Zn0.5Fe2O4 (Ni50) nanoparticles at different frequencies, χ′ vs. T|f. We found that the relative peak temperature variation per frequency decade, ϕ=∆TT·∆log(f)—a known measure of interparticle interaction strength—exhibits a four-fold increase, from ϕ = 0.04 in Ni50 to ϕ = 0.16 in Ni25. This corresponds to a fundamental change in the nanoparticles’ superspin dynamics, as proven by the fit of phenomenological models to magnetic relaxation data. Indeed, the Ni25 ensemble exhibits superparamagnetic behavior, where the temperature dependence of the superspin relaxation time, τ, is described in the Dorman–Bessais–Fiorani (DBF) model: τT=τrexp⁡EB+EadkBT, with parameters τr = 4 × 10−12 s, and (EB + Ead)/kB = 1473 K. On the other hand, the nanoparticles in the Ni50 ensemble freeze collectively upon cooling in a spin-glass fashion according to a critical dynamics law: τ(T)=τ0TTg−1zν, with τ0 = 4 × 10−8 s, Tg = 145 K, and zν = 7.2. Rietveld refinements against powder X-ray diffraction data reveal the structural details that underlie the observed magnetic behavior: an indirect cation replacement mechanism by which non-magnetic Zn ions are incorporated in the tetrahedral sites of the inverse spinel.

The effect of swift heavy ion irradiation on sol–gel-prepared maghemite nanoparticles was studied by 57Fe transmission Mössbauer spectroscopy and X-ray diffractometry (XRD). The room temperature Mössbauer spectra of the non-irradiated nano-maghemite showed poorly resolved magnetically split, typical relaxation spectra due to the superparamagnetic state of the nanoparticles. Significant changes in the line shape, indicating changes in the superparamagnetic state, were found in the Mössbauer spectra upon irradiation by 160 MeV and 155 MeV 132Xe26+ ions with fluences of 5 × 1013 ion cm−2 and 1 × 1014 ion cm−2. XRD of the irradiated maghemite nanoparticles showed a significant broadening of the corresponding lines, indicating a decrease in the crystallite size, compared to those of the non-irradiated ones. The results are discussed in terms of the defects induced by irradiation and the corresponding changes related to the change in particle size and consequently in the superparamagnetic state caused by irradiation.

This study aimed to develop multifunctional nanoplatforms for both cancer imaging and therapy using superparamagnetic iron oxide nanoparticles (SPIONs). Two distinct synthetic methods, reduction–precipitation (MR/P) and co-precipitation at controlled pH (MpH), were explored, including the assessment of the coating’s influence, namely dextran and gold, on their magnetic properties. These SPIONs were further functionalized with gadolinium to act as dual T1/T2 contrast agents for magnetic resonance imaging (MRI). Parameters such as size, stability, morphology, and magnetic behavior were evaluated by a detailed characterization analysis. To assess their efficacy in imaging and therapy, relaxivity and hyperthermia experiments were performed, respectively. The results revealed that both synthetic methods lead to SPIONs with similar average size, 9 nm. Mössbauer spectroscopy indicated that samples obtained from MR/P consist of approximately 11–13% of Fe present in magnetite, while samples obtained from MpH have higher contents of 33–45%. Despite coating and functionalization, all samples exhibited superparamagnetic behavior at room temperature. Hyperthermia experiments showed increased SAR values with higher magnetic field intensity and frequency. Moreover, the relaxivity studies suggested potential dual T1/T2 contrast agent capabilities for the coated SPpH-Dx-Au-Gd sample, thus demonstrating its potential in cancer diagnosis.

The strong ferromagnetic nanoparticles are analyzed within the band structure-based shell model, accounting for discrete quantum levels of conducting electrons. As is demonstrated, such an approach allows for the description of the observed superparamagnetic features of these nanocrystals. Assemblies of such superparamagnets incorporated into nonmagnetic insulators, semiconductors, or metallic substrates are shown to display ferromagnetic coupling, resulting in a superferromagnetic ordering at sufficiently dense packing. Properties of such metamaterials are investigated by making use of the randomly jumping interacting moments model, accounting for quantum fluctuations induced by the discrete electronic levels and disorder. Employing the mean-field treatment for such superparamagnetic assemblies, we obtain the magnetic state equation, indicating conditions for an unstable behavior. Respectively, magnetic spinodal regions and critical points occur on the magnetic phase diagram of such ensembles. The respective magnetodynamics exhibit jerky behavior expressed as erratic stochastic jumps in magnetic induction curves. At critical points, magnetodynamics displays the features of self-organized criticality. Analyses of magnetic noise correlations are proposed as model-independent analytical tools employed in order to specify, quantify, and analyze the magnetic structure and origin of superferromagnetism. We discuss some results for a sensor-mode application of superferromagnetic reactivity associated with spatially local external fields, e.g., the detection of magnetic particles. The transport of electric charge carriers between superparamagnetic particles is considered tunneling and Landau-level state dynamics. The tunneling magnetoresistance is predicted to grow noticeably with decreasing nanomagnet size. The giant magnetoresistance is determined by the ratio of the respective times of flight and relaxation and can be significant at room temperature. Favorable designs for superferromagnetic systems with sensor implications are revealed.

The present manuscript portrays environmental benign, cost‐effective and energy efficient green route way to synthesize Mg−Zn ferrite nanoparticles [Mg0.05Zn0.05Fe2O4 NPs] using Ocimum Basilicum leaf extract [OBLE]. X‐ray diffraction (XRD) analysis revealed that Ocimum Basilicum leaf extract mediated Mg−Zn ferrite nanoparticles [OBLE@Mg−Zn NPs] exhibit face centred cubic crystallinity with space group Fd3‾m ${{\rm F}{\rm d}\bar{3}{\rm m}}$ as confirmed by Rietveld refinement studies. Microstructural analysis illustrated uniform surface morphology with well interlinked grain with an average grain size of 35.6±0.12 nm. FTIR spectra showed existence of hydroxyl −OH group at 3403 cm−1 and C=C vibration at 2345 cm−1. Magnetic hysteresis loop (M−H loop) confirmed the superparamagnetic behaviour of OBLE@Mg−Zn NPs. Cytotoxic activity of OBLE@Mg−Zn NPs was carried out against breast cancer cell line MDA‐MB‐231. Dose dependent cell viability of cancerous cells depicted cytotoxic potential of OBLE@Mg−Zn NPs. [ABSTRACT FROM AUTHOR]

The strong ferromagnetic nanoparticles are analyzed within the band structure-based shell model, accounting for discrete quantum levels of conducting electrons. As is demonstrated, such an approach allows for the description of the observed superparamagnetic features of these nanocrystals. Assemblies of such superparamagnets incorporated into nonmagnetic insulators, semiconductors, or metallic substrates are shown to display ferromagnetic coupling, resulting in a superferromagnetic ordering at sufficiently dense packing. Properties of such metamaterials are investigated by making use of the randomly jumping interacting moments model, accounting for quantum fluctuations induced by the discrete electronic levels and disorder. Employing the mean-field treatment for such superparamagnetic assemblies, we obtain the magnetic state equation, indicating conditions for an unstable behavior. Respectively, magnetic spinodal regions and critical points occur on the magnetic phase diagram of such ensembles. The respective magnetodynamics exhibit jerky behavior expressed as erratic stochastic jumps in magnetic induction curves. At critical points, magnetodynamics displays the features of self-organized criticality. Analyses of magnetic noise correlations are proposed as model-independent analytical tools employed in order to specify, quantify, and analyze the magnetic structure and origin of superferromagnetism. We discuss some results for a sensor-mode application of superferromagnetic reactivity associated with spatially local external fields, e.g., the detection of magnetic particles. The transport of electric charge carriers between superparamagnetic particles is considered tunneling and Landau-level state dynamics. The tunneling magnetoresistance is predicted to grow noticeably with decreasing nanomagnet size. The giant magnetoresistance is determined by the ratio of the respective times of flight and relaxation and can be significant at room temperature. Favorable designs for superferromagnetic systems with sensor implications are revealed. [ABSTRACT FROM AUTHOR]

A series of organically coated iron oxide nanoparticles obtained via the thermal decomposition of iron–oleate complexes via a "heating-up" process were investigated using the methods of transmission electron microscopy, X-ray diffraction and fine magnetometry, accompanied by elaborate mathematical analysis. The analysis of dependencies of field dependencies on the magnetization of the shape and broadening of maxima of X-ray diffraction patterns and fine refinement of transmission electron microscopy data allowed us to demonstrate that all of the samples under consideration had a tripartite structure: (i) the magnetic crystalline core of iron oxide, (ii) the paramagnetic stratum of amorphous iron oxide and (iii) the organic coater. The new approach toward synthesis for organic coated iron oxide shows that it could be applied to the preparation of magnetic nanoparticles with different and controlled magnetic properties and sizes depending on necessary applications, especially biomedical. [ABSTRACT FROM AUTHOR]

Maghemite (γ-Fe2O3) nanoparticles were synthesized via a sol–gel process with (Fe(NO3)3 9H2O) as a starting material and annealed in an Ar/H2 (5%) balanced gas atmosphere. According to x-ray analysis, the average particle size was found to be 7.0 nm with a narrow size distribution for samples annealed at 150°C. Transmission electron microscopy (TEM) analysis also confirmed a particle size of 7.2 nm. The structural and magnetic properties were analyzed using x-ray diffraction (XRD), vibrating-sample magnetometry (VSM), and Mössbauer spectroscopy, and were found to have a spinel structure and exhibit superparamagnetic behavior. TEM was carried out to monitor the size and morphology of the particles. The hyperfine fields at 4.2 K for the A and B sites were determined to be 509 kOe and 476 kOe, respectively. The isomer shift values were δB = 0.36 mm/s and δA = 0.32 mm/s, which both correspond to Fe3+. Since magnetite (Fe3O4) has Fe2+ and maghemite has only Fe3+, it can be seen from the Mössbauer result that the powder heat-treated at 150°C is maghemite. The blocking temperature (TB) of the superparamagnetic maghemite nanoparticles was approximately 167 ± 5 K. The magnetic anisotropy constant was calculated to be 1.4 × 106 ergs/cm3. The coercivity value at 0 K was calculated as HCO = 174.5 Oe. [ABSTRACT FROM AUTHOR]

The orientation of hydroxyapatite whiskers ( HAw ) is one of key to design and develop bioactive ceramics for bone regeneraction. Guided behavior based on the construction of magnetic anisotropy. In this study, magnetic nanoparticles Fe3O4 were loaded onto the surface of HAw by hydrothermal method, and magnetic HAw composites with excellent magnetic response characteristics were successfully prepared. The physicochemical properties and biological properties of magnetized HAw were systematically studied, and its orientation behavior in weak magnetic field was explored. The results show that ferric oxide ( Fe3 O4) nanoparticles are successfully loaded onto the surface of HAw, and the magnetized HAw has superparamagnetism and good magnetic response at room temperature, which can be manupulated by conventional permanent magnets. The alignment direction applied by the external magnetic field is effectively fixed by combining the magnetic field-induced grouting molding technology. The results of CCK-8 experiment show that magnetized HAw has no cytotoxicity. [ABSTRACT FROM AUTHOR]

The AC magnetic properties of a sample of Fe3O4 nanoparticles coated with oleic acid have been investigated with the help of AC susceptibility measurements. In particular, several DC magnetic fields have been superimposed on the AC field, and their effect on the magnetic response of the sample has been analysed. The results show the presence of a double peak structure in the imaginary component of the complex AC susceptibility measured as a function of the temperature. A preliminary evaluation of the Mydosh parameter for both peaks gives the information that each one of them is associated with a different state of interaction between nanoparticles. The two peaks evolve both in amplitude and position when the intensity of the DC field is changed. The field dependence of the peak position shows two different trends, and it is possible to study them in the framework of the currently existing theoretical models. In particular, a model of non-interacting magnetic nanoparticles has been used to describe the behaviour of the peak at lower temperatures, whereas the behaviour of the peak at higher temperatures has been analysed in the framework of a spin-glass-like model. The proposed analysis technique can be useful for the characterisation of magnetic nanoparticles used in several types of applications, such as biomedical and magnetic fluids. [ABSTRACT FROM AUTHOR]

The effect of sodium chloride (NaCl) on the magnetism of nanopowders of the spinel ferrite (MgFe2O4) produced using a salt-assisted solution combustion synthesis was investigated. X-ray diffraction (XRD) analysis was conducted to evaluate crystalline structure and phase composition of the synthesized materials. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to evaluate the particle size and morphology. Magnetic behavior was analyzed by measuring and analyzing the respective hysteresis loops using a vibrating sample magnetometer (VSM). The characterization showed that the presence of NaCl affects the phase composition, size, and dispersion of the nanoparticles, as well as their magnetic behavior. The theoretical size of the nanoparticles was calculated using the Scherrer equation, obtaining sizes of about 21.07 nm for the nanoparticles without salt, 5.90 nm for the sample salt content of 1.7 mol and 6.48 nm—for 3.4 mol. The synthesized nanoparticles showed a drastic decrease in coercivity field, remanence, and saturation with increasing salt content. Therefore, the salt content is a crucial parameter in controlling the morphology and magnetic properties of the nanoparticles obtained by the solution combustion route. [ABSTRACT FROM AUTHOR]

We present results of magneto-optical investigations of (CoFeZr) x (Al2O 3 ) 1 0 0 − x film nanocomposites in transverse Kerr effect (TKE) geometry in the spectral range 0.5–4.0 eV and magnetic field up to 3.0 kOe. Nanocomposites were deposited onto a glass-ceramic substrate by ion-beam sputtering. The TKE response at room temperature strongly depends on the wavelength of light, applied magnetic field H and the volume metallic fraction. From the analysis of the field dependences of TKE at different wavelengths, it follows that in the as-deposited samples, the interaction between nanoparticles at x < 3 0 at.% is small and the nanocomposite is an ensemble of superparamagnetic particles; as x increases to 32 at.%, a superspinglass-type state arises, then, in the vicinity of 34 at.%, along with individual superparamagnetic particles, superferromagnetic regions appear. Long-range ferromagnetic order arises at concentrations x less than the percolation threshold for conductivity x per = 4 2. 6 at.%. In the presence of two different magnetic states in the samples, TKE is not proportional to the magnetization. Both the field dependences at near-infrared region and the spectral dependences of TKE change significantly after annealing of the samples, while the changes in the field dependences of the magnetization are almost imperceptibly. [ABSTRACT FROM AUTHOR]

Ti3C2Tx–Fe3O4–carbon nanotube composites were prepared for electrochemical energy storage in the negative electrodes of supercapacitors. The electrodes show a remarkably high areal capacitance of 6.59 F cm−2 in a neutral Na2SO4 electrolyte, which was obtained by the development of advanced nanofabrication strategies and due to the synergistic effect of the individual components. Enhanced capacitance was achieved using the in-situ synthesis method for the Fe3O4 nanoparticles. The superparamagnetic behavior of the Fe3O4 nanoparticles facilitated the fabrication of electrodes with a reduced binder content. Good mixing of the components was achieved using a celestine blue co-dispersant, which adsorbed on the inorganic components and carbon nanotubes and facilitated their co-dispersion and mixing. The capacitive behavior was optimized by the variation of the electrode composition and mass loading in a range of 30–45 mg cm−2. An asymmetric device was proposed and fabricated, which contained a Ti3C2Tx–Fe3O4–carbon nanotube negative electrode and a polypyrrole–carbon nanotube positive electrode for operation in an Na2SO4 electrolyte. The asymmetric supercapacitor device demonstrated high areal capacitance and excellent power-density characteristics in an enlarged voltage window of 1.6 V. This investigation opens a new avenue for the synthesis and design of MXene-based asymmetric supercapacitors for future energy storage devices. [ABSTRACT FROM AUTHOR]

CoFe2O4 nanocrystals were synthesized through chemical co-precipitation using citric acid as the capping agent. Subsequently, a green alternative was accomplished in the synthesis process by replacing the commercially purchased citric acid with naturally available lemon juice. The prepared samples were thoroughly characterized using various techniques, and the results were analyzed and the parametric variations in the two samples were compared. Using Rietveld profile refinement of the XRD patterns, the crystallographic parameters associated with both samples were explored and the cation distributions in the tetrahedral and octahedral sites were estimated. Williamson–Hall analysis of x-ray diffraction data provided the effective crystallite size and the microstrain associated with the nanocrystalline samples. The optical direct band gap and the room-temperature magnetic parameters were estimated from UV–visible spectra analysis and vibrating sample magnetometry, respectively. The coercivity, remanent magnetization, and saturation magnetization of both samples were obtained from magnetic hysteresis, and the estimated values for magnetic anisotropy energy revealed that the samples exhibited room-temperature ferrimagnetic behavior. [ABSTRACT FROM AUTHOR]