Reduction-Induced Magnetic Behavior in LaFeO3-δ Thin Films

The effect of oxygen reduction on the magnetic properties of LaFeO3-δ (LFO) thin films was studied to better understand the viability of LFO as a candidate for magnetoionic memory. Differences in the amount of oxygen lost by LFO and its magnetic behavior were observed in nominally identical LFO films grown on substrates prepared using different common methods. In an LFO film grown on as-received SrTiO3 (STO) substrate, the original perovskite film structure was preserved following reduction, and remnant magnetization was only seen at low temperatures. In a LFO film grown on annealed STO, the LFO lost significantly more oxygen and the microstructure decomposed into La- and Fe-rich regions with remnant magnetization that persisted up to room temperature. These results demonstrate an ability to access multiple, distinct magnetic states via oxygen reduction in the same starting material and suggest LFO may be a suitable materials platform for nonvolatile multistate memory.

Unraveling Exchange Coupling in Ferrites Nano-Heterostructures

The magnetic coupling of a set of SrFe12 O19 /CoFe2 O4 nanocomposites is investigated. Advanced electron microscopy evidences the structural coherence and texture at the interfaces of the nanostructures. The fraction of the lower anisotropy phase (CoFe2 O4 ) is tuned to assess the limits that define magnetically exchange-coupled interfaces by performing magnetic remanence, first-order reversal curves (FORCs), and relaxation measurements. By combining these magnetometry techniques and the structural and morphological information from X-ray diffraction, electron microscopy, and Mössbauer spectrometry, the exchange intergranular interaction is evidenced, and the critical thickness within which coupled interfaces have a uniform reversal unraveled.

Investigation of Structural, Dielectric and Optical Properties of Polyaniline-Magnesium Ferrite Composites

A study on the influence of magnesium ferrite nanoparticles on the optical and dielectric attributes of Polyaniline has been conducted. Magnesium nano Ferrite powder is synthesized by the self-propagating solution combustion method. Polyaniline-Magnesium nano ferrite composites are synthesized by chemical oxidative polymerization of aniline with the addition of Magnesium nanoparticles. The samples are characterized with XRD and UV-Vis spectrometer, in the wavelength range of 200-800 nm and studied for optical properties. Dielectric properties are studied in the frequency range of 50 Hz to 5 MHz. X-ray diffraction reveals single phase formation of Magnesium ferrite, whereas Polyaniline shows an amorphous nature. In the XRD of the composites, we see the crystalline peaks of ferrite becoming more intense with the addition of ferrite and whereas the peak of Polyaniline diminishes. The crystallite size is quantified with the Debye-Scherrer formula, and it increases as the content of ferrite in the composites increases. The micro-strain decreases in the composites as the percentage of ferrite enhances in the composites. In the UV-Vis absorption spectra of composites, the peaks of Polyaniline shift to higher wavelength and there is also an absorption band in the spectra of composites corresponding to that of Magnesium ferrite particles. Both direct and indirect band gaps are calculated with the Tauc plot, and both the optical band gap decrease as the percentage of ferrite increases in the composite. The dielectric loss and dielectric constant both decrease with frequency in all the samples, and the dielectric response are in good agreement with Maxwell-Wagner model. Ferrite-polymer composites with both conducting and magnetic properties are considered useful for electromagnetic shielding and microwave absorption.

Remanence Increase in SrFe12O19/Fe Exchange-Decoupled Hard-Soft Composite Magnets Owing to Dipolar Interactions

In the search for improved permanent magnets, fueled by the geostrategic and environmental issues associated with rare-earth-based magnets, magnetically hard (high anisotropy)-soft (high magnetization) composite magnets hold promise as alternative magnets that could replace modern permanent magnets, such as rare-earth-based and ceramic magnets, in certain applications. However, so far, the magnetic properties reported for hard-soft composites have been underwhelming. Here, an attempt to further understand the correlation between magnetic and microstructural properties in strontium ferrite-based composites, hard SrFe₁₂O₁₉ (SFO) ceramics with different contents of Fe particles as soft phase, both in powder and in dense injection molded magnets, is presented. In addition, the influence of soft phase particle dimension, in the nano- and micron-sized regimes, on these properties is studied. While Fe and SFO are not exchange-coupled in our magnets, a remanence that is higher than expected is measured. In fact, in composite injection molded anisotropic (magnetically oriented) magnets, remanence is improved by 2.4% with respect to a pure ferrite identical magnet. The analysis of the experimental results in combination with micromagnetic simulations allows us to establish that the type of interaction between hard and soft phases is of a dipolar nature, and is responsible for the alignment of a fraction of the soft spins with the magnetization of the hard. The mechanism unraveled in this work has implications for the development of novel hard-soft permanent magnets.

Fabrication of High-Performance Asymmetric Supercapacitors Using Rice Husk-Activated Carbon and MnFe2O4 Nanostructures

To meet the growing demand for efficient and sustainable power sources, it is crucial to develop high-performance energy storage systems. Additionally, they should be cost-effective and able to operate without any detrimental environmental side effects. In this study, rice husk-activated carbon (RHAC), which is known for its abundance, low cost, and excellent electrochemical performance, was combined with MnFe₂O₄ nanostructures to improve the overall capacitance of asymmetric supercapacitors (ASCs) and their energy density. A series of activation and carbonization steps are involved in the fabrication process for RHAC from rice husk. Furthermore, the BET surface area for RHAC was determined to be 980 m² g^-1 and superior porosities (average pore diameter of 7.2 nm) provide abundant active sites for charge storage. Additionally, MnFe₂O₄ nanostructures were effective pseudocapacitive electrode materials due to their combined Faradic and non-Faradic capacitances. In order to assess the electrochemical performance of ASCs extensively, several characterization techniques were employed, including galvanostatic charge -discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Comparatively, the ASC demonstrated a maximum specific capacitance of ~420 F/g at a current density of 0.5 A/g. The as-fabricated ASC possesses remarkable electrochemical characteristics, including high specific capacitance, superior rate capability, and long-term cycle stability. The developed asymmetric configuration retained 98% of its capacitance even after 12,000 cycles performed at a current density of 6A/g, demonstrating its stability and reliability for supercapacitors. The present study demonstrates the potential of synergistic combinations of RHAC and MnFe₂O₄ nanostructures in improving supercapacitor performance, as well as providing a sustainable method of using agricultural waste for energy storage.

Engineered Polyethylene Glycol-Coated Zinc Ferrite Nanoparticles as a Novel Magnetic Resonance Imaging Contrast Agent

Polyethylene glycol (PEG) was utilized to functionalize the surface of zinc ferrite nanoparticles (NPs) synthesized by the hydrothermal process in order to prevent aggregation and improve the biocompatibility of the NPs for the proposed magnetic resonance imaging (MRI) agent. Various spectroscopy techniques were used to examine the NPs' structure, size, morphology, and magnetic properties. The NPs had a cubic spinel structure with an average size of 8 nm. The formations of the spinel ferrite and the PEG coating band at the ranges of 300-600 and 800-2000 cm^-1, respectively, were validated by Fourier-transform infrared spectroscopy. The NPs were spherical in shape, and energy-dispersive X-ray spectroscopy with mapping confirmed the presence of zinc, iron, and oxygen in the samples. The results of high-resolution transmission electron microscopy revealed an average size of 14 nm and increased stability after PEG coating. The decrease in zeta potential from -24.5 to -36.5 mV confirmed the PEG coating on the surface of the NPs. A high saturation magnetization of ∼50 emu/g, measured by vibration sample magnetometer, indicated the magnetic potential of NPs for biomedical applications. An MTT assay was used to examine the cytotoxicity and viability of human normal skin cells (HSF 1184) exposed to zinc ferrite and PEG@Zn ferrite NPs at various concentrations. After 24 h of treatment, negligible cytotoxicity of PEG-coated NPs was observed at high concentrations. Magnetic resonance imaging (MRI) suggested that PEG@Zn ferrite NPs are a unique and perfectly suited contrast agent for T₂-weighted MRI and can successfully enhance the image contrast.

Potassium Ferrite for Biomedical Applications

Ferrites have been widely studied for their use in the biomedical area, mostly due to their magnetic properties, which gives them the potential to be used in diagnostics, drug delivery, and in treatment with magnetic hyperthermia, for example. In this work, KFeO₂ particles were synthesized with a proteic sol-gel method using powdered coconut water as a precursor; this method is based on the principles of green chemistry. To improve its properties, the base powder obtained was subjected to multiple heat treatments at temperatures between 350 and 1300 °C. The samples obtained underwent structural, morphological, biocompatibility, and magnetic characterization. The results show that upon raising the heat treatment temperature, not only is the wanted phase detected, but also the secondary phases. To overcome these secondary phases, several different heat treatments were carried out. Using scanning electron microscopy, grains in the micrometric range were observed. Saturation magnetizations between 15.5 and 24.1 emu/g were observed for the samples containing KFeO₂ with an applied field of 50 kOe at 300 K. From cellular compatibility (cytotoxicity) assays, for concentrations up to 5 mg/mL, only the samples treated at 350 °C were cytotoxic. However, the samples containing KFeO₂, while being biocompatible, had low specific absorption rates (1.55-5.76 W/g).

Metal and Metal Oxides Nanoparticles and Nanosystems in Anticancer and Antiviral Theragnostic Agents

The development of antiviral treatment and anticancer theragnostic agents in recent decades has been associated with nanotechnologies, and primarily with inorganic nanoparticles (INPs) of metal and metal oxides. The large specific surface area and its high activity make it easy to functionalize INPs with various coatings (to increase their stability and reduce toxicity), specific agents (allowing retention of INPs in the affected organ or tissue), and drug molecules (for antitumor and antiviral therapy). The ability of magnetic nanoparticles (MNPs) of iron oxides and ferrites to enhance proton relaxation in specific tissues and serve as magnetic resonance imaging contrast agents is one of the most promising applications of nanomedicine. Activation of MNPs during hyperthermia by an external alternating magnetic field is a promising method for targeted cancer therapy. As therapeutic tools, INPs are promising carriers for targeted delivery of pharmaceuticals (either anticancer or antiviral) via magnetic drug targeting (in case of MNPs), passive or active (by attaching high affinity ligands) targeting. The plasmonic properties of Au nanoparticles (NPs) and their application for plasmonic photothermal and photodynamic therapies have been extensively explored recently in tumor treatment. The Ag NPs alone and in combination with antiviral medicines reveal new possibilities in antiviral therapy. The prospects and possibilities of INPs in relation to magnetic hyperthermia, plasmonic photothermal and photodynamic therapies, magnetic resonance imaging, targeted delivery in the framework of antitumor theragnostic and antiviral therapy are presented in this review.

A thorough Investigation of Rare-Earth Dy3+ Substituted Cobalt-Chromium Ferrite and Its Magnetoelectric Nanocomposite

The stoichiometric compositions of a ferrite system with a chemical formula CoCr_0.5Dy_xFe_1.5-xO₄ where x = 0.0, 0.025, 0.05, 0.075 and 0.1 were prepared by the sol-gel auto-combustion method. The structural, morphological and magnetic properties were studied by the X-ray diffraction (XRD), infra-red spectroscopy (IR), scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometer. XRD analysis confirmed the cubic spinel structure of the prepared samples without the presence of any impurity and secondary phases. Selected area electron diffraction and IR measurements gives further confirmation to the XRD observations. Considering that strain mechanism, elastic properties and cation distribution play a major role for controlling the magnetic properties and therefore these properties were precisely evaluated through reliable methodologies such as XRD and IR data. The cation distribution was determined by the X-ray diffraction data which are further supported by the magnetization studies. Magnetoelectric properties of CoCr_0.5Dy_xFe_1.5-xO₄ + BaTiO₃ have also been investigated. The mechanisms involved are discussed in the manuscript.

Simultaneous Enhancement of Magnetothermal and Photothermal Responses by Zn, Co Co-Doped Ferrite Nanoparticles

Reducing nanoparticle (NP) dosage for hyperthermia therapy has remained a great challenge. In this work, efficiencies of alternating current (AC) magnetic field and near-infrared (NIR) heating are simultaneously enhanced by Zn and Co co-doping of magnetite NPs. The optimum magnetic anisotropy for maximized loss power under each magnetic field is achieved by tuning the doping concentration. The specific loss power of Zn_0.3 Co_0.08 Fe_2.62 O₄ @SiO₂ NPs reaches 2428 W g^-1 under an AC field of 27 kA m^-1 at 430 kHz; 12 296 W g^-1 under NIR laser irradiation at 808 nm and 2.5 W cm^-2 ; and an unprecedented value of 14 724 W g^-1 under dual mode. These values far exceed what has been achieved previously in iron oxide NPs. Ex vivo experiments on sacrificial mice show that while the NP dosage is substantially reduced to that used for magnetic resonance imaging, the surface body temperature of the mice reaches 50 °C after exposure to both AC field and laser irradiation under field parameters and laser intensity below safety limits. This nanoplatform is thus promising for multi-modal local hyperthermia therapy.

MXene/Ferrite Magnetic Nanocomposites for Electrochemical Supercapacitor Applications

MXene has been identified as a new emerging material for various applications including energy storage, electronics, and bio-related due to its wider physicochemical characteristics. Further the formation of hybrid composites of MXene with other materials makes them interesting to utilize in multifunctional applications. The selection of magnetic nanomaterials for the formation of nanocomposite with MXene would be interesting for the utilization of magnetic characteristics along with MXene. However, the selection of the magnetic nanomaterials is important, as the magnetic characteristics of the ferrites vary with the stoichiometric composition of metal ions, particle shape and size. The selection of the electrolyte is also important for electrochemical energy storage applications, as the electrolyte could influence the electrochemical performance. Further, the external magnetic field also could influence the electrochemical performance. This review briefly discusses the synthesis method of MXene, and ferrite magnetic nanoparticles and their composite formation. We also discussed the recent progress made on the MXene/ferrite nanocomposite for potential applications in electrochemical supercapacitor applications. The possibility of magnetic field-assisted supercapacitor applications with electrolyte and electrode materials are discussed.

Wideband Microwave Photonic Circulator Using Two Asymmetric Partial-Height Triangle Ferrites

Broadband 5G communication requires the operation of nonreciprocal devices in the Ku band. A wideband photonic crystal circulator is implemented by introducing two partial-height triangular Ni-Zn ferrites into the Al₂O₃ ceramic rod-arrays. The asymmetric sizes of the two equilateral triangles paired with self-matching effectively extend the bandwidth of the circulator eight times over that of the symmetric scheme. Numerical simulations demonstrate that the photonic crystal circulator can obtain a bandwidth of 1.00 GHz with an isolation 25.75 dB and an insertion loss 0.381 dB through optimized matched triangle size ratio, suitable for applications in future communication systems.

Combined Effect of Microstructure, Surface Energy, and Adhesion Force on the Friction of PVA/Ferrite Spinel Nanocomposites

Nanocomposite films based on spinel ferrite (Mg_0.8Zn_0.2Fe_1.5Al_0.5O₄) in a PVA matrix were obtained. An increase in the spinel concentration to 10 wt.% caused an avalanche-like rise in roughness due to the formation of nanoparticle agglomerates. The lateral mode of atomic force microscopy (AFM) allowed us to trace the agglomeration dynamics. An unexpected result was that the composite with 6 wt.% of filler had a low friction coefficient in comparison with similar composites due to the successfully combined effects of low roughness and surface energy. The friction coefficient decreased to 0.07 when the friction coefficient of pure PVA was 0.72. A specially developed method for measuring nano-objects' surface energy using AFM made it possible to explain the anomalous nature of the change in tribological characteristics.

The Cation Distributions of Zn-doped Normal Spinel MgFe2O4 Ferrite and Its Magnetic Properties

Determining the exact occupation sites of the doping ions in spinel ferrites is vital for tailoring and improving their magnetic properties. In this study, the distribution and occupation sites of cations in MgFe₂O₄ and Zn-doped MgFe₂O₄ ferrite are imaged by Cs-STEM. The experimental STEM images along [001], [011] and [111] orientations suggest that the divalent Mg²⁺ cations occupy all A sites, and the trivalent Fe³⁺ cations occupy all B sites in MgFe₂O₄ ferrite prepared by electrospinning, which is consistent with the normal spinel structure. We further clarify that the preferred sites of dopant Zn²⁺ ions are Fe³⁺ crystallographic sites in the Zn-doped MgFe₂O₄ ferrite nanofibers. Magnetic measurements show that Zn doping affects the spin states of the Fe³⁺, and the Fe³⁺-O²⁻-Fe³⁺ super-exchange interaction leads to enhancements in the magnetization and reduction in the Curie temperature. Our work should contribute a significant step toward eventually realizing the practical application of doped spinel ferrites.

Doping Independent Work Function and Stable Band Gap of Spinel Ferrites with Tunable Plasmonic and Magnetic Properties

Tuning optical or magnetic properties of nanoparticles, by addition of impurities, for specific applications is usually achieved at the cost of band gap and work function reduction. Additionally, conventional strategies to develop nanoparticles with a large band gap also encounter problems of phase separation and poor crystallinity at high alloying degree. Addressing the aforementioned trade-offs, here we report Ni-Zn nanoferrites with energy band gap (E_g) of ≈3.20 eV and a work function of ≈5.88 eV. While changes in the magnetoplasmonic properties of the Ni-Zn ferrite were successfully achieved with the incorporation of bismuth ions at different concentrations, there was no alteration of the band gap and work function in the developed Ni-Zn ferrite. This suggests that with the addition of minute impurities to ferrites, independent of their changes in the band gap and work function, one can tune their magnetic and optical properties, which is desired in a wide range of applications such as nanobiosensing, nanoparticle based catalysis, and renewable energy generation using nanotechnology.

Coexistence and Coupling of Multiple Charge Orderings and Spin States in Hexagonal Ferrite

The coupling between charge and spin orderings in strongly correlated systems plays a crucial role in fundamental physics and device applications. As a candidate of multiferroic materials, LuFe₂O₄ with a nominal Fe^2.5+ valence state has the potential for strong charge-spin interactions; however, these interactions have not been fully understood until now. Here, combining complementary characterization methods with theoretical calculations, two types of charge orderings with distinct magnetic properties are revealed. The ground states of LuFe₂O₄ are decided by the parallel/antiparallel coupling of both charge and spin orderings in the adjacent FeO double layers. Whereas the ferroelectric charge ordering remains ferrimagnetic below 230 K, the antiferroelectric ordering undergoes antiferromagnetic-ferrimagnetic-paramagnetic transitions from 2 K to room temperature. This study demonstrates the unique aspects of strong spin-charge coupling within LuFe₂O₄. Our results shed light on the coexistence and competing nature of orderings in quantum materials.

Recent Advances in Synthesis and Applications of MFe2O4 (M = Co, Cu, Mn, Ni, Zn) Nanoparticles

In the last decade, research on the synthesis and characterization of nanosized ferrites has highly increased and a wide range of new applications for these materials have been identified. The ability to tailor the structure, chemical, optical, magnetic, and electrical properties of ferrites by selecting the synthesis parameters further enhanced their widespread use. The paper reviews the synthesis methods and applications of MFe₂O₄ (M = Co, Cu, Mn, Ni, Zn) nanoparticles, with emphasis on the advantages and disadvantages of each synthesis route and main applications. Along with the conventional methods like sol-gel, thermal decomposition, combustion, co-precipitation, hydrothermal, and solid-state synthesis, several unconventional methods, like sonochemical, microwave assisted combustion, spray pyrolysis, spray drying, laser pyrolysis, microemulsion, reverse micelle, and biosynthesis, are also presented. MFe₂O₄ (M = Co, Cu, Mn, Ni, Zn) nanosized ferrites present good magnetic (high coercivity, high anisotropy, high Curie temperature, moderate saturation magnetization), electrical (high electrical resistance, low eddy current losses), mechanical (significant mechanical hardness), and chemical (chemical stability, rich redox chemistry) properties that make them suitable for potential applications in the field of magnetic and dielectric materials, photoluminescence, catalysis, photocatalysis, water decontamination, pigments, corrosion protection, sensors, antimicrobial agents, and biomedicine.

Effect of Chemical Composition on Magnetic and Electrical Properties of Ferroelectromagnetic Ceramic Composites

In this paper, ferroelectric-ferrimagnetic ceramic composites based on multicomponent PZT-type (PbZr_1-xTi_xO₃-type) material and ferrite material with different percentages in composite compositions were obtained and studied. The ferroelectric component of the composite was a perovskite ceramic material with the chemical formula Pb_0.97Bi_0.02(Zr_0.51Ti_0.49)_0.98(Nb_2/3Mn_1/3)_0.02O₃ (P), whereas the magnetic component was nickel-zinc ferrite with the chemical formula Ni_0.5Zn_0.5Fe₂O₄ (F). The process of sintering the composite compounds was carried out by the free sintering method. Six ferroelectric-ferrimagnetic ceramic P-F composite compounds were designed and obtained with different percentages of its components, i.e., 90/10 (P90-F10), 85/15 (P85-F15), 80/20 (P80-F20), 60/40 (P60-F40), 40/60 (P40-F60), and 20/80 (P20-F80). X-ray diffraction patterns, microstructural, ferroelectric, dielectric, magnetic properties, and DC electrical conductivity of the composite materials were investigated. In this study, two techniques were used to image the microstructure of P-F composite samples: SB (detection of the signals from the secondary and backscattered electron detectors) and BSE (detection of backscattered electrons), which allowed accurate visualization of the presence and distribution of the magnetic and ferroelectric component in the volume of the composite samples. The studies have shown that at room temperature, the ceramic composite samples exhibit good magnetic and electrical properties. The best set of physical properties and performance of composite compositions have ceramic samples with a dominant phase of ferroelectric component and a small amount of the ferrite component (P90-F10). Such a composition retains the high ferroelectric properties of the ferroelectric component in the composite while also acquiring magnetic properties. These properties can be prospectively used in new types of memory and electromagnetic converters.

Decrease in the Crystallite Diameter of Solid Crystalline Magnetite around the Curie Temperature by Microwave Magnetic Fields Irradiation

A decrease in the crystallite diameter of ferrites irradiated with microwaves has been considered as a non-thermal effect of so-called de-crystallization; however, its mechanism has not been elucidated. We hypothesized that a decrease in the crystallite diameter is caused by interaction between the ordered spins of ferrite and the magnetic field of microwaves. To verify this, we focused on magnetite with a Curie temperature of 585 °C. Temperature dependence around this temperature and time dependence of the crystallite diameter of the magnetite irradiated with microwaves at different temperatures and durations were investigated. From the X-ray diffraction data, the crystallite diameter of magnetite exhibited a minimum value at 500 °C, just below the Curie temperature of magnetite, where the energy loss of the interaction between magnetite's spins and the microwaves takes the maximum value. The crystallite diameter exhibited a minimum value at 5 min irradiation time, during which the microwaves were excessively absorbed. Transmission electron microscopy observations showed that the microstructure of irradiated magnetite in this study was different from that reported previously, indicating that a decrease in the crystallite diameter is not caused by de-crystallization but its similar phenomenon. A decrease in coercivity and lowering temperature of Verwey transition were observed, evidencing decreased crystallite diameter. This study can thus contribute to the development of the theory of a non-thermal effect.

Structural, Optical and Electrical Properties of Cu0.6CoxZn0.4-xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) Soft Ferrites

A series of cobalt-inserted copper zinc ferrites, Cu_0.6Co_xZn_0.4−xFe₂O₄ (x = 0.0, 0.1, 0.2, 0.3, 0.4) having cubic spinel structure were prepared by the coprecipitation method. Various characterization techniques, including XRD, FTIR, UV-vis and I–V were used to investigate structural optical and electrical properties, respectively. The lattice constant was observed to be decreased as smaller ionic radii Co²⁺ (0.74 Å) replaced the higher ionic radii Zn²⁺ (0.82 Å). The presence of tetrahedral and octahedral bands was confirmed by FTIR spectra. Optical bandgap energy was determined in the range of 4.44–2.05 eV for x = 0.0 to 0.4 nanoferrites, respectively. DC electrical resistivity was measured and showed an increasing trend (5.42 × 10⁸ to 6.48 × 10⁸ Ω·cm) with the addition of cobalt contents as cobalt is more conductive than zinc. The range of DC electrical resistivity (10⁸ ohm-cm) makes these nanomaterials potential candidates for telecommunication devices.

Multifunctional Properties of Binary Polyrhodanine Manganese Ferrite Nanohybrids-From the Energy Converters to Biological Activity

The PRHD@MnFe₂O₄ binary hybrids have shown a potential for applications in the biomedical field. The polymer cover/shell provides sufficient surface protection of magnetic nanoparticles against adverse effects on the biological systems, e.g., it protects against Fenton’s reactions and the generation of highly toxic radicals. The heating ability of the PRHD@MnFe₂O₄ was measured as a laser optical density (LOD) dependence either for powders as well as nanohybrid dispersions. Dry hybrids exposed to the action of NIR radiation (808 nm) can effectively convert energy into heat that led to the enormous temperature increase ΔT 170 °C (>190 °C). High concentrated colloidal suspensions (5 mg/mL) can generate ΔT of 42 °C (65 °C). Further optimization of the nanohybrids amount and laser parameters provides the possibility of temperature control within a biologically relevant range. Biological interactions of PRHD@MnFe₂O₄ hybrids were tested using three specific cell lines: macrophages (RAW 264.7), osteosarcoma cells line (UMR-106), and stromal progenitor cells of adipose tissue (ASCs). It was shown that the cell response was strongly dependent on hybrid concentration. Antimicrobial activity of the proposed composites against Escherichia coli and Staphylococcus aureus was confirmed, showing potential in the exploitation of the fabricated materials in this field.

Synthesis of manganese doped β-FeOOH and MnFe2O4 nanorods for enhanced drug delivery and hyperthermia application

Preparation of manganese ferrite (MnFe2O4) nanorods by the reduction of akaganeite seeds in the presence of oleylamine is reported. The Mn-doped β-FeOOH akaganeite seeds have been processed by the hydrolysis of metal-chloride salts in the presence of polyethylenimine (PEI) surfactant. The hydrophobic oleylamine capped nanorods are made hydrophilic using trisodium citrate as a phase transferring agent. The nanorods form with an aspect ratio of 5.47 and possess a high magnetisation value of 69 emu/g at an applied magnetic field of 1.5 T. The colloidal water dispersion of nanorods exhibits superior heating efficiency by the application of alternating magnetic field (AMF). A specific absorption rate value of 798 W/g is achieved at an applied AMF of field strength 500 Oe and frequency 316 kHz. Further, the citrate functionalised nanorods are capable of attaching with doxorubicin (DOX) electrostatically with a loading efficiency of 97% and the drug release is pH responsive. The DOX loaded nanorods show a promising effect on the apoptosis of MCF-7 as experimented in vitro.

Long-Term Colloidally Stable Aqueous Dispersions of ≤5 nm Spinel Ferrite Nanoparticles

Applications in biomedicine and ferrofluids, for instance, require long-term colloidally stable, concentrated aqueous dispersions of magnetic, biocompatible nanoparticles. Iron oxide and related spinel ferrite nanoparticles stabilized with organic molecules allow fine-tuning of magnetic properties via cation substitution and water-dispersibility. Here, we synthesize≤5 nm iron oxide and spinel ferrite nanoparticles, capped with citrate, betaine and phosphocholine, in a one-pot strategy. We present a robust approach combining elemental (CHN) and thermal gravimetric analysis (TGA) to quantify the ratio of residual solvent molecules and organic stabilizers on the particle surface, being of particular accuracy for ligands with heteroatoms compared to the solvent. SAXS experiments demonstrate the long-term colloidal stability of our aqueous iron oxide and spinel ferrite nanoparticle dispersions for at least 3 months. By the use of SAXS we approved directly the colloidal stability of the nanoparticle dispersions for high concentrations up to 100 g L-1.

Investigation of AC-Measurements of Epoxy/Ferrite Composites

A pure ferrite and epoxy samples as well as the epoxy/ferrite composites with different 20 wt.%, 30 wt.%, 40 wt.%, and 50 wt.% weight ferrite contents have been prepared by the chemical co-precipitation method. AC-conductivity and dielectric properties such as the dielectric constant and dielectric loss of the prepared samples have been studied. The obtained results showed that the samples had a semiconductor behavior. The dielectric constant of the composites has been calculated theoretically using several models. For the composite sample that contains 20 wt.% of ferrites, these models give satisfactory compliance, while for the composite samples with a higher percentage of nanofillers, more than 30 wt.% theoretical results do not coincide with experimental data. The investigated polymer has very low conductivity, so this type of polymer can be useful for high-frequency applications, which can reduce the losses caused by eddy current. Thus, the prepared samples are promising materials for practical use as elements of microwave devices.

Synthesis and Properties of Nanosized Stoichiometric Cobalt Ferrite Spinel

Nanoparticles with controllable sizes of ferrite spinel CoFe₂O₄ were formed by thermal treatment of cobalt-iron glycerolate. Thermal behavior during the heating was studied by differential thermal analysis combined with thermogravimetry. The precursor, as well as the prepared nanoparticles, were analyzed by a broad spectrum of analytic techniques (X-Ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD), Energy dispersive spectroscopy (EDS), Atomic absorption spectroscopy (AAS), Scanning electron microscopy (SEM), and Raman spectroscopy). The particle size of nanoparticles was obtained from Transmission electron microscopy and also calculated using Scherrer formula. A vibrating sample magnetometer (VSM) in a Physical Property Measurement System was used to analyze the magnetic properties of nanoparticles.

HSA loaded with CoFe2 O4 /MNPs as a high‐efficiency carrier for epirubicin anticancer drug delivery

Drug delivery is one of the most important challenges in the domain of health. Non‐toxic and biocompatible carriers are provided by human serum albumin nano‐capsule (HSA/NC) for drug delivery applications. In this study, HSA, with high loadings of drug‐modified cobalt ferrite (CoFe2 O4) magnetic nanoparticle (CoFe2 O4 /MNPs) was fabricated for epirubicin anticancer drug delivery. In the initial step, CoFe2 O4 /MNPs was synthesised via co‐precipitation technique and characterised by X‐ray powder diffraction, vibrating sample magnetometry, energy dispersive X‐ray analysis, scanning electron microscopy and map analysis. Furthermore, CoFe2 O4 /MNPs and epirubicin were loaded into HSA/NC and utilised as a novel system against breast cancer cell line (MCF‐7). IC50 for free epirubicin, unloaded CoFe2 O4 /MNPs/HSA/NC, CoFe2 O4 /MNPs and epirubicin‐loaded CoFe2 O4 /MNPs/HSA/NC were 7.7, 2400, 840 and 430 μg/ml, respectively. The results obtained revealed high cytotoxicity effect of epirubicin‐loaded CoFe2 O4 /MNPs on breast cancer cell line.

Microwave Absorption and the Magnetic Hyperthermia Applications of Li0.3Zn0.3Co0.1Fe2.3O4 Nanoparticles in Multiwalled Carbon Nanotube Matrix

Nanoparticles of Li_0.3Zn_0.3Co_0.1Fe_2.3O₄ (LZC) were prepared by the sol-gel method and dried in a furnace at ∼200 °C. The dried sample was annealed at 500, 600, 700, and 800 °C for 5 h each. Rietveld analysis of X-ray diffraction patterns confirms the cubic Fd3̅m phase formation with lattice parameters ranged from 8.376 up to 8.390 Å and allows the crystallite sizes (d_cryst) to be estimated. To enhance microwave (MW) absorption as well as the effectiveness for hyperthermia treatment, nanoparticles are taken in the matrix of multiwalled carbon nanotubes (MWCNTs) and the morphology of the so-prepared samples (LZC@MWCNT) was studied by scanning electron microscopy and transmission electron microscopy analyses. Both static and dynamic magnetic properties were investigated on the samples of LZC nanoparticles and compared to those of the samples of LZC@MWCNT. The samples annealed at 500, 600, and 800 °C are excellent candidates in cancer treatment as ac magnetic heating analysis shows that the hyperthermia temperature (42 °C) was successfully achieved for an applied ac magnetic field of 420 Oe and 300 kHz frequency. MW absorption study also reveals that the samples of LZC@MWCNT could be used as a potential MW absorbing material for which a maximum reflection loss (R_L) of ∼-21 dB was achieved at a frequency of 15.27 GHz for only 1 mm layer thickness.

Employing Calcination as a Facile Strategy to Reduce the Cytotoxicity in CoFe2O4 and NiFe2O4 Nanoparticles

CoFe₂O₄ and NiFe₂O₄ nanoparticles (NPs) represent promising candidates for biomedical applications. However, in these systems, the knowledge over how various physical and chemical parameters influence their cytotoxicity remains limited. In this article, we investigated the effect of different calcination temperatures over cytotoxicity of CoFe₂O₄ and NiFe₂O₄ NPs, which were synthesized by a sol-gel proteic approach, toward L929 mouse fibroblastic cells. More specifically, we evaluated and compared CoFe₂O₄ and NiFe₂O₄ NPs presenting low crystallinity (that were calcined at 400 and 250 °C, respectively) with their highly crystalline counterparts (that were calcined at 800 °C). We found that the increase in the calcination temperature led to the reduction in the concentration of surface defect sites and/or more Co or Ni atoms located at preferential crystalline sites in both cases. A reduction in the cytotoxicity toward mouse fibroblast L929 cells was observed after calcination at 800 °C. Combining with inductively coupled plasma mass spectrometry data, our results indicate that the calcination temperature can be employed as a facile strategy to reduce the cytotoxicity of CoFe₂O₄ and NiFe₂O₄, in which higher temperatures contributed to the decrease in the dissolution of Co²⁺ or Ni²⁺ from the NPs. We believe these results may shed new insights into the various parameters that influence cytotoxicity in ferrite NPs, which may pave the way for their widespread applications in biomedicine.

The effect of magnetic nanoparticles on neuronal differentiation of induced pluripotent stem cell-derived neural precursors

Introduction

Magnetic resonance (MR) imaging is suitable for noninvasive long-term tracking. We labeled human induced pluripotent stem cell-derived neural precursors (iPSC-NPs) with two types of iron-based nanoparticles, silica-coated cobalt zinc ferrite nanoparticles (CZF) and poly-l-lysine-coated iron oxide superparamagnetic nanoparticles (PLL-coated γ-Fe₂O₃) and studied their effect on proliferation and neuronal differentiation.

Materials and methods

We investigated the effect of these two contrast agents on neural precursor cell proliferation and differentiation capability. We further defined the intracellular localization and labeling efficiency and analyzed labeled cells by MR.

Results

Cell proliferation was not affected by PLL-coated γ-Fe₂O₃ but was slowed down in cells labeled with CZF. Labeling efficiency, iron content and relaxation rates measured by MR were lower in cells labeled with CZF when compared to PLL-coated γ-Fe₂O₃. Cytoplasmic localization of both types of nanoparticles was confirmed by transmission electron microscopy. Flow cytometry and immunocytochemical analysis of specific markers expressed during neuronal differentiation did not show any significant differences between unlabeled cells or cells labeled with both magnetic nanoparticles.

Conclusion

Our results show that cells labeled with PLL-coated γ-Fe₂O₃ are suitable for MR detection, did not affect the differentiation potential of iPSC-NPs and are suitable for in vivo cell therapies in experimental models of central nervous system disorders.

Temperature-Dependent Magnetic Response of Antiferromagnetic Doping in Cobalt Ferrite Nanostructures

In this work Mn_xCo_1−xFe₂O₄ nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400–4000 cm⁻¹ which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe₂O₄) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field.

High-Performance Ferrite Nanoparticles through Nonaqueous Redox Phase Tuning

From magnetic resonance imaging to cancer hyperthermia and wireless control of cell signaling, ferrite nanoparticles produced by thermal decomposition methods are ubiquitous across biomedical applications. While well-established synthetic protocols allow for precise control over the size and shape of the magnetic nanoparticles, structural defects within seemingly single-crystalline materials contribute to variability in the reported magnetic properties. We found that stabilization of metastable wüstite in commonly used hydrocarbon solvents contributed to significant cation disorder, leading to nanoparticles with poor hyperthermic efficiencies and transverse relaxivities. By introducing aromatic ethers that undergo radical decomposition upon thermolysis, the electrochemical potential of the solvent environment was tuned to favor the ferrimagnetic phase. Structural and magnetic characterization identified hallmark features of nearly defect-free ferrite nanoparticles that could not be demonstrated through postsynthesis oxidation with nearly 500% increase in the specific loss powers and transverse relaxivity times compared to similarly sized nanoparticles containing defects. The improved crystallinity of the nanoparticles enabled rapid wireless control of intracellular calcium. Our work demonstrates that redox tuning during solvent thermolysis can generate potent theranostic agents through selective phase control in ferrites and can be extended to other transition metal oxides relevant to memory and electrochemical storage devices.

Bifunctional Modification of Graphitic Carbon Nitride with MgFe2O4 for Enhanced Photocatalytic Hydrogen Generation

To gain high photocatalytic activity for hydrogen evolution, both charge separation efficiency and surface reaction kinetics must be improved, and together would be even better. In this study, the visible light photocatalytic hydrogen production activity of graphitic carbon nitride (g-C3N4) was greatly enhanced with MgFe2O4 modification. It was demonstrated that MgFe2O4 could not only extract photoinduced holes from g-C3N4, leading to efficient charge carrier separation at the g-C3N4/MgFe2O4 interface, but also act as an oxidative catalyst accelerating the oxidation reaction kinetics at g-C3N4 surface. This dual function of MgFe2O4 thus contributed to the great improvement (up to three-fold) in photocatalytic activity for hydrogen generation over g-C3N4/MgFe2O4 as compared to pristine g-C3N4, after loading Pt by photoreduction method. It was revealed that in the Pt/g-C3N4/MgFe2O4 system, the photoinduced electrons and holes were entrapped by Pt and MgFe2O4, respectively, giving rise to the promoted charge separation; moreover, as evidenced by electrochemical analysis, the electrocatalysis effect of MgFe2O4 benefited the oxidation reaction at g-C3N4 surface.

Ferrite core non-linearity in coils for magnetic neurostimulation

The need to correctly predict the voltage across terminals of mm-sized coils, with ferrite core, to be employed for magnetic stimulation of the peripheral neural system is the motivation for this work. In such applications, which rely on a capacitive discharge on the coil to realise a transient voltage curve of duration and strength suitable for neural stimulation, the correct modelling of the non-linearity of the ferrite core is critical. A demonstration of how a finite-difference model of the considered coils, which include a model of the current-controlled inductance in the coil, can be used to correctly predict the time-domain voltage waveforms across the terminals of a test coil is presented. Five coils of different dimensions, loaded with ferrite cores, have been fabricated and tested: the measured magnitude and width of the induced pulse are within 10% of simulated values.

Tuning the magnetic properties of metal oxide nanocrystal heterostructures by cation exchange

For three types of colloidal magnetic nanocrystals, we demonstrate that postsynthetic cation exchange enables tuning of the nanocrystal's magnetic properties and achieving characteristics not obtainable by conventional synthetic routes. While the cation exchange procedure, performed in solution phase approach, was restricted so far to chalcogenide based semiconductor nanocrystals, here ferrite-based nanocrystals were subjected to a Fe(2+) to Co(2+) cation exchange procedure. This allows tracing of the compositional modifications by systematic and detailed magnetic characterization. In homogeneous magnetite nanocrystals and in gold/magnetite core shell nanocrystals the cation exchange increases the coercivity field, the remanence magnetization, as well as the superparamagnetic blocking temperature. For core/shell nanoheterostructures a selective doping of either the shell or predominantly of the core with Co(2+) is demonstrated. By applying the cation exchange to FeO/CoFe(2)O(4) core/shell nanocrystals the Neél temperature of the core material is increased and exchange-bias effects are enhanced so that vertical shifts of the hysteresis loops are obtained which are superior to those in any other system.

Magnetic properties of liquid-phase sintered CoFe₂O₄ for application in magnetoelastic and magnetoelectric transducers

Cobalt ferrite is a ferrimagnetic magnetostrictive ceramic that has potential application in magnetoelastic and magnetoelectric transducers. In this work, CoFe(2)O(4) was obtained using a conventional ceramic method and Bi(2)O(3) was used as additive in order to obtain liquid-phase sintered samples. Bi(2)O(3) was added to the ferrite in amounts ranging from 0.25 mol% to 0.45 mol% and samples were sintered at 900 °C and 950 °C. It was observed the presence of Bi-containing particles in the microstructure of the sintered samples and the magnetostriction results indicated microstructural anisotropy. It was verified that it is possible to get dense cobalt ferrites, liquid-phase sintered, with relative densities higher than 90% and with magnetostriction values very close to samples sintered without additives.

Low temperature-fired Ni-Cu-Zn ferrite nanoparticles through auto-combustion method for multilayer chip inductor applications

Ferrite nanoparticles of basic composition Ni0.7-xZnxCu0.3Fe2O4 (0.0 ≤ x ≤ 0.2, x = 0.05) were synthesized through auto-combustion method and were characterized for structural properties using X-ray diffraction [XRD], scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy [FT-IR]. XRD analysis of the powder samples sintered at 600°C for 4 h showed the cubic spinel structure for ferrites with a narrow size distribution from 28 to 32 nm. FT-IR showed two absorption bands (v1 and v2) that are attributed to the stretching vibration of tetrahedral and octahedral sites. The effect of Zn doping on the electrical properties was studied using dielectric and impedance spectroscopy at room temperature. The dielectric parameters (ε', ε″, tanδ, and σac) show their maximum value for 10% Zn doping. The dielectric constant and loss tangent decrease with increasing frequency of the applied field. The results are explained in the light of dielectric polarization which is similar to the conduction phenomenon. The complex impedance shows that the conduction process in grown nanoparticles takes place predominantly through grain boundary volume.PACS: 75.50.Gg; 78.20; 77.22.Gm.

Microstructural and Mössbauer properties of low temperature synthesized Ni-Cd-Al ferrite nanoparticles

We report the influence of Al3+ doping on the microstructural and Mössbauer properties of ferrite nanoparticles of basic composition Ni0.2Cd0.3Fe2.5 - xAlxO4 (0.0 ≤ x ≤ 0.5) prepared through simple sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray, transmission electron microscopy (TEM), Fourier transformation infrared (FTIR), and Mössbauer spectroscopy techniques were used to investigate the structural, chemical, and Mössbauer properties of the grown nanoparticles. XRD results confirm that all the samples are single-phase cubic spinel in structure excluding the presence of any secondary phase corresponding to any structure. SEM micrographs show the synthesized nanoparticles are agglomerated but spherical in shape. The average crystallite size of the grown nanoparticles was calculated through Scherrer formula and confirmed by TEM and was found between 2 and 8 nm (± 1). FTIR results show the presence of two vibrational bands corresponding to tetrahedral and octahedral sites. Mössbauer spectroscopy shows that all the samples exhibit superparamagnetism, and the quadrupole interaction increases with the substitution of Al3+ ions.