High Saturation Magnetization Research Articles

Preparation and characterization of various PVPylated divalent metal-doped ferrite nanoparticles for magnetic hyperthermia.

There is an incessant demand to keep improving on the heating responses of polymeric magnetic nanoparticles (MNPs) under magnetic excitation, particularly in the pursuit for them to be utilized for clinical hyperthermia applications. Herein, we report the fabrication of a panel of PVP-capped divalent metal-doped MFe2O4 (M ≅ Co, Ni, Zn, Mg, and Sn) MNPs prepared via the Ko-precipitation Hydrolytic Basic (KHB) methodology and assess their magneto-thermal abilities. The physiochemical, structural, morphological, compositional, and magnetic properties of the doped ferrites were fully characterized using various techniques mainly TEM, XRD, EDX, FTIR, and VSM. The obtained doped MNPs exhibited stabilized quasi-spherical sized particles (10-17 nm), pure well-crystallized cubic spinel phases, and high saturation magnetizations (Ms = 26-81 emu g-1). In response to a clinically-safe alternating magnetic field (AMF) (f = 332.8 kHz and H = 170 Oe), distinctive heating responses of these doped ferrites were attained. Hyperthermia temperatures of 42 °C can be reached very fast in only ∼5 min, with heating temperatures slowly increasing to reach up to 55 °C. The highest heating performance was observed for PVP-NiFe2O4 and the lowest for PVP-Sn-doped NPs (SAR values: PVP-NiFe2O4 > PVP-CoFe2O4 > PVP-ZnFe2O4 > PVP-MgFe2O4 > PVP-SnFe2O4). This trend was found to be directly correlated to their observed magnetic saturation and anisotropy. Heating efficiencies and specific SAR values as functions of concentration, frequency, and amplitude were also systematically investigated. Finally, cytotoxicity assay was conducted on aqueous dispersions of the doped ferrite NPs, proving their biocompatibility and safety profiles. The PVPylated metal-doped ferrite NPs prepared here, particularly Ni- and Co-doped ferrites, are promising vehicles for potential combined magnetically-triggered biomedical hyperthermia applications.

Streamlined Synthesis of Clopidogrel Utilizing Magnetically Recyclable Fe3O4 Nanoparticles through the Strecker Reaction

Aim: The study explores the use of magnetite nanoparticles for eco-friendly α-aminonitrile synthesis via the Strecker reaction, aiming to provide a more efficient, cost-effective, and sustainable method. Methods: The research involves an extensive exploration of magnetite nanoparticles, belonging to the inverse spinel group, as catalysts for the Strecker reaction. The magnetic properties of Fe3O4 nanoparticles facilitate their easy removal from reaction masses using an external magnet, eliminating the need for conventional filtration or centrifugation methods. Trimethylsilyl cyanide (TMSCN) is utilized as a cyanide ion source, known for its efficiency and user-friendly characteristics, aiming to enhance the eco-friendliness of the synthesis. Results: Magnetite nanoparticles with FCC oxygen arrangement and Fe2+ and Fe3+ ions show potential applications in medical and organometallic chemistry. High saturation magnetization, low toxicity, and biocompatibility make them promising for drug delivery and MRI contrast agents. Conclusion: The research presents an environmentally friendly Strecker reaction method using Fe3O4 nanoparticles, offering a promising alternative to traditional methods for α-aminonitrile synthesis and demonstrating the potential of magnetite nanoparticles.

Novel multi-magnetic material transcranial magnetic stimulation coils for small animals application

Transcranial magnetic stimulation (TMS) is a non-invasive therapeutic approach with proven efficacy in treating certain psychiatric and neurological disorders. To broaden the application of TMS to a wider range of neurological disorders, the induced electric field (e-field) must be able to more focally target specific regions of the brain. Animal coil designs are promising for studying TMS effects and developing new procedures for treating various neurological and psychiatric disorders. However, investigations have mostly used coil designs intended for humans, and, as such, have failed to scale down for small animal sizes. Currently available coil systems have been limited by not adequately incorporating ideal soft magnetic materials as coil cores and not advancing the coil shapes for small animals as is necessary to achieve highly focused e-field concentration. In this study, we used multi-magnetic materials in TMS coils for the first time to our knowledge. We also considered the non-linear, hysteretic behavior of the cores in our FEM simulations of induced e-field and magnetic field in the brain models of the rat. Our study involved a comprehensive assessment of the distribution and intensity of the e-field across various coil configurations using our customized anatomically accurate rat head model. Iron-cobalt-vanadium (Permendur) alloy known for its high relative permeability, high saturation magnetization and low coercivity was used as the core material for all simulations. To enhance coil focality and concentration of the e-field, while avoiding stimulation of adjacent regions, we introduced a shape-conforming, flexible, diamagnetic pyrolytic graphite with susceptibility of -4.5×10-4 for our top performing coil. Simulation results were validated by comparing the simulated magnetic field results with experimental measurements obtained from the v-tip coil with a carbon steel AISI-1010 core at varying tip distances. This thorough study advances our knowledge of TMS coil designs and their optimization, particularly for small animal applications.

Unveiling the crystal and magnetic texture of iron oxide nanoflowers.

Iron oxide nanoflowers (IONF) are densely packed multi-core aggregates known for their high saturation magnetization and initial susceptibility, as well as low remanence and coercive field. This study reports on how the local magnetic texture originating at the crystalline correlations among the cores determines the special magnetic properties of individual IONF over a wide size range from 40 to 400 nm. Regardless of this significant size variation in the aggregates, all samples exhibit a consistent crystalline correlation that extends well beyond the IONF cores. Furthermore, a nearly zero remnant magnetization, together with the presence of a persistently blocked state, and almost temperature-independent field-cooled magnetization, support the existence of a 3D magnetic texture throughout the IONF. This is confirmed by magnetic transmission X-ray microscopy images of tens of individual IONF, showing, in all cases, a nearly demagnetized state caused by the vorticity of the magnetic texture. Micromagnetic simulations agree well with these experimental findings, showing that the interplay between the inter-core direct exchange coupling and the demagnetizing field is responsible for the highly vortex-like spin configuration that stabilizes at low magnetic fields and appears to have partial topological protection. Overall, this comprehensive study provides valuable insights into the impact of crystalline texture on the magnetic properties of IONF over a wide size range, offering a deeper understanding of their potential applications in fields such as biomedicine and water remediation.

Structural, thermodynamic, and magnetic properties of SrFe12O19 hexaferrite modified by co-substitution of Cu and Gd.

A hard magnetic system of SrFe12O19 nanomaterial was modified according to the composition of Sr0.95Gd0.05Fe12-xCuxO19 with x = 0.0, 0.30, and 0.60 using the sol-gel technique. The structures of the samples were evaluated using X-ray diffraction (XRD) along with Rietveld refinement, and an M-type hexaferrite with a hexagonal structure was confirmed with a trace amount of the α-Fe2O3 phase. In addition, transmission electron microscopy (TEM) analysis revealed polycrystalline nanoplates in all samples. Furthermore, the bond structures of the octahedral and tetrahedral sites along with the thermodynamic properties of these ferrites were extracted from the FTIR spectra at room temperature. The Debye temperature (θD) decreased from 755.9 K to 749.3 K due to the co-substitution of Gd3+ at Sr2+ and Cu2+ at Fe3+. The magnetic hysteresis (M-H) measurements revealed that the coercivity decreased from 5.3 kOe to 1.5 kOe along with the highest magnetization saturation (Ms) of 65.2 emu g-1 for the composition Sr0.95Gd0.05Fe11.7Cu0.3O19, which is suitable for industrial application. The effect of local crystalline anisotropy in magnetization was explored using the law of approach to saturation (LAS). Finally, thermo-magnetization was recorded in the range from 400 K to 5 K for cooling under zero field and in the presence of a 100 Oe field, and magnetic transitions were tracked due to the introduction of the foreign atoms of Gd and Cu into SrFe12O19.

Enhancement in the dielectric and magnetic properties of Ni2+-Cu2+ co-doped BaFe11Cu1-xNixO19 hexaferrites (0.0 ≤ x ≤ 1.0).

Herein, Ni2+-Cu2+ co-doped barium hexaferrites (BaFe11Cu1-xNixO19, 0.0 ≤ x≤ 1.0 with an interval of 0.25) were successfully synthesized using a co-precipitation method. The formation of a magnetoplumbite structure with the P63/mmc space group was confirmed by Rietveld refinement of the obtained X-ray diffraction patterns. Microstructural investigations revealed grains in the shape of hexagonal plates, while co-doping resulted in a variation in the grain sizes of the prepared samples. X-ray photoelectron spectroscopy was performed to determine the valence state of iron in the prepared hexaferrites. Impedance spectroscopy analysis revealed that dielectric permittivity initially decreased with an increase in the co-dopant content up to x = 0.5 and then increased by two orders of magnitude for x = 1.0. Alternatively, resistive properties showed microstructural resistance values in the range 105-108 Ω, with the highest value obtained for the sample with x = 0.5. Furthermore, magnetic measurements indicated that all the prepared samples exhibited ferrimagnetic behaviour. Saturation magnetization and magnetic anisotropy values were found to be the highest for the sample with x = 1.0, which also had the lowest coercivity among the prepared samples. Herein, the observed variations in the obtained results can be explained by the variations in grain sizes and the Fe2+/Fe3+ ratio associated with the preferential occupation of co-dopants at octahedral sites. Based on our findings, the BaFe11Ni1O19 (x = 1.0) composition appears to be the most promising choice as a microwave absorption material among the prepared samples owing to the coexistence of high dielectric permittivity (>103 at 107 Hz) and saturation magnetization (73 emu g-1).

Facile one-pot synthesis of the mesoporous chitosan-coated cobalt ferrite nanozyme as an antibacterial and MRI contrast agent.

Cobalt ferrite (CoFe) nanoparticles (NPs) with appropriate physicochemical and biological properties have attracted great attention for biomedical applications. In the present study, chitosan-coated mesoporous CoFe (CoFeCH) NPs were synthesized using a facile one-step hydrothermal method and fully characterized using FE-SEM, EDS, BET, FTIR spectroscopy, DLS, TGA, XRD, and VSM. The spherical, highly colloidal, and monodispersed CoFeCH NPs with an average hydrodynamic size of 177.9 nm, PDI of 0.238 and zeta potential value of -33 represented a high saturation magnetization value of 59.37 emu g-1. N2 adsorption-desorption analysis confirmed the mesoporous structure of CoFeCH NPs with a type IV isotherm, calculated specific surface area of 89.583 m2 g-1 and total pore volume of 0.3668 cm3 g-1. CoFeCH NPs exhibited high antibacterial effects on S. aureus and E. coli, comparable with standard antibiotics, while CH-coating led to higher biocompatibility of CoFe NPs on human cells in vitro. CoFeCH NPs also showed significant peroxidase activity with a Km value of 14.37 and specific activity of 0.632 mmol min-1. CoFeCH NPs were successfully used as a MRI contrast agent with an R2 value of 91.3 mM-1 s-1. The overall results indicated the high potential of synthesized CoFeCH NPs by the present method for biomedical applications, especially as an antibacterial and MRI contrast agent.

Hard magnetic properties of Fe16N2 magnets

Fe16N2 nanopowder composed of the α″-Fe16N2 phase exhibited a high saturation magnetization of 168 emu/g and a relatively high coercivity of 2.65 kOe under magnetic measurements with a DC magnetic field of 25 kOe at room temperature. A thermal study revealed that the α″-Fe16N2 phase in the Fe16N2 nanopowder was thermally stable up to 539 K. Fe16N2 nanopowder is, therefore, a prospective candidate for rare-earth-free magnets.

Single-domain Fe2CoGa0.5Al0.5 Heusler alloy nanoparticles with enhanced properties.

Fine quaternary single-domain Heusler alloy nanoparticles with a composition of Fe2CoGa0.5Al0.5 have been synthesized using a simple template-less chemical route for the first time. Ab initio calculations and standard models have been used to analyze and interpret the experimental findings. The synthesized nanoparticles with an average crystallite size of 42 nm exhibited high saturation magnetization (>5 μB f.u.-1), high effective anisotropy constant (≈8 × 106 erg cc-1), high Curie temperature (>1200 K), low magnetic remanence (<0.2 μB f.u.-1) and low coercive field (<90 Oe), declaring their suitability for fabricating various nanomagnetic devices.

Extracorporeal Blood Treatment Using Functional Magnetic Nanoclusters Mitigates Organ Dysfunction of Sepsis in Swine.

Mitigating sepsis-induced severe organ dysfunction with magnetic nanoparticles has shown remarkable advances in extracorporeal blood treatment. Nevertheless, treating large septic animals remains challenging due to insufficient magnetic separation at rapid blood flow rates (>6 L h-1) and limited incubation time in an extracorporeal circuit. Herein, superparamagnetic nanoclusters (SPNCs) coated with red blood cell (RBC) membranes are developed, which promptly capture and magnetically separate a wide range of pathogens at high blood flow rates in a swine sepsis model. The SPNCs exhibited an ultranarrow size distribution of clustered iron oxide nanocrystals and exceptionally high saturation magnetization (≈ 90 emu g-1) close to that of bulk magnetite. It is also revealed that CD47 on the RBCs allows the RBC-SPNCs to remain at a consistent concentration in the blood by evading innate immunity. The uniform size distribution of the RBC-SPNCs greatly enhances their effectiveness in eradicating various pathogenic materials in extracorporeal blood. The use of RBC-SPNCs for extracorporeal treatment of swine infected with multidrug-resistant E. coli is validated and found that severe bacteremic sepsis-induced organ dysfunction is significantly mitigated after 12 h. The findings highlight the potential application of RBC-SPNCs for extracorporeal therapy of severe sepsis in large animal models and potentially humans.

Narrow Band Gap and High Saturation Magnetization in Y-Doped NiCo Ferrites

Narrow Band Gap and High Saturation Magnetization in Y-Doped NiCo Ferrites

Multiple enhancement on the magnetic and electric properties of SrM hexaferrites by phase-change perovskite additives

M−type strontium (SrM) hexaferrites, which possess a high saturation magnetization, coercivity, and maximum magnetic energy product, have been widely used as permanent magnets in electric machines. However, emerging high-speed and high-power electric machines put forward higher requirements on the loss characteristics of ferrites at high frequencies and high temperatures. Here, the effects of two phase-change perovskite additives, barium titanate (BTO) and BTO-based ceramic with a positive temperature coefficient (PTCC), on the magnetic properties, electrical properties, and their temperature dependence of SrM hexaferrite are reported. The spatial concentration distribution and diffusion kinetics of the perovskite additives are investigated, showing their accumulation at the grain boundaries and gradual diffusion into the crystallites. Due to the high melting points, the addition of BTO and PTCC at the grain boundaries hinder the grain growth and reduce the grain size. Due to the strong pinning effect of the impurities near the grain boundaries and the reduction of grain size, enhancement in coercivity up to 10 % as well as an increase of 225 % in resistivity are observed. More interestingly, a positive temperature dependence of the resistivity is achieved by adding various amounts of PTCC. These results demonstrate the capability of phase-change perovskite additives to achieve simultaneous enhancement in multiple electromagnetic and temperature properties of SrM hexaferrite.

Highly ordered single domain Fe2-xCo1+xGa (0 ≤ x ≤ 1) nanoparticles synthesized by a template-less chemical route

A comprehensive study has been carried out on chemically synthesized Fe2-xCo1+xGa (0 ≤ x ≤ 1) nanoparticles using both experimental and theoretical tools. Adoption of a template-free preparation route ensured impurity-free and phase-pure Heusler alloy nanoparticles. Depending on the composition, these nanoparticles exhibit highly ordered L21 or X type Heusler alloy structure. These nanoparticles have high saturation magnetization (3.90 – 5.15 µB/f.u.), high Curie temperature (≥ 1100 K) and high effective anisotropy constant (∼ 106 erg/cc) along with low coercive field (≤ 12 Oe) and low remnant magnetization (≤ 0.03 µB/f.u.). Emergence of superparamagnetism in these single (magnetic) domain nanoparticles is another interesting aspect. The electronic density of states of these alloys near Fermi level have also been evaluated as a function of composition using ab initio calculations. These results indicate Fe2-xCo1+xGa nanoparticles to be promising candidates for high density magnetic media and nanomagnetic sensor applications.

A comprehensive study on MnZn ferrite materials with high saturation magnetic induction intensity and high permeability for magnetic field energy harvesting

Manganese-zinc (MnZn) ferrites have important applications in energy conversion, transmission, and harvesting. MnZn ferrite for magnetic field energy harvesting is expected to enhance the saturation magnetic induction (Bs), initial permeability (μi), and Curie temperature (Tc) aspects simultaneously, which is beneficial to the energy harvesting efficiency and safety of the device. In this paper, various formulations of MnZn ferrite samples were prepared by the conventional oxide ceramic process. The cation distribution was determined through Rietveld refinement of XRD patterns Based on this, the M–T curves were fitted by combining Néel molecular field theory with Brillouin functions. The greatest influence on the Curie temperature was found to be the molecular field coefficient between the A and B sites. The magnetization mechanism of MnZn ferrite was comprehensively analyzed by fitting the complex permeability spectrum, magnetocrystalline anisotropy constant, and magnetostriction coefficient. The ratio of domain wall displacement magnetization to domain rotation magnetization shows an increasing and then decreasing trend with Fe content, while |K1| shows an opposite trend. Finally, MnZn ferrite materials with excellent overall performance (Bs = 505mT, μi = 9016, Tc = 447 K) were prepared by investigating the magnetization mechanism.

Optimizing Annealing Temperature Control for Enhanced Magnetic Properties in Fe-Si-B Amorphous Flake Powder Cores

In this study, we examined the optimal pre- and post-annealing conditions for soft magnetic composites (SMCs) using amorphous flake powders produced through ball milling of amorphous Fe-Si-B ribbons, leading to enhanced magnetic properties. The SMCs, which utilized flake powders created via melt spinning, displayed outstanding DC bias characteristics, as well as increased permeability, primarily due to high saturation magnetization and the flaky morphology of the powders. Pre-annealing was performed not only to remove residual stress formed during the melt spinning process but also to improve pulverizing efficiency, which ultimately affected the particle size of the flake powders. Core annealing was performed to reduce core losses and improve permeability by relieving the residual stress generated during the pressing process. As a result, pre-annealing and core annealing temperatures were identified as crucial factors influencing the magnetic properties of the SMCs. We meticulously analyzed the particle size, the morphology of the flake powder, and the magnetic properties of the SMCs in relation to the annealing temperatures. In conclusion, we demonstrated that flake powder SMCs achieved superior soft magnetic properties, including significantly reduced core loss and heightened permeability, through optimal pre- and core-annealing at 370 °C and 425 °C, respectively.

A joint strategy for CO2 reduction and CH3OH oxidation at electrode to CO + CH4 and methylal in ionic liquid

Electrochemical reduction reaction of CO2 (CO2eRR) in aqueous electrolyte currently encounters with sluggish oxygen evolution at anode and hydrogen evolution as a competing reaction at cathode. A Cu-FeOx-N-doped carbon composite (CFCN) prepared by facile pyrolysis of Cu-Fe salts and melamine was used as cathode, associated with Pt sheet anode to perform CO2eRR to CO + CH4 and partial oxidation of methanol to methylal (DMM) in ionic liquid-methanol electrolyte solution. The electrolysis exhibits efficient red-ox activity with higher average FEDMM (59.9%) for DMM within 24 h and high momentary FEC1 (87.2%) for CO + CH4 at 24 h, specifically, realizing red-ox reactions couple for synchronously producing high-valued chemicals, DMM and CO + CH4. Besides, the composite also demonstrates high saturation magnetization (110 emu/g). The catalytic role and contribution of the various components such as metal Cu, CuOx and Fe3O4 nanocrystallines constituting the composite for CO2eRR and to magnetic property were examined. The catalyst possesses high run stability for CO2eRR as the electrolysis has continuously performed for 120 h.

Investigation of crystal structure, Raman spectroscopy and magnetic properties of La-Zn substituted oriented M-type hexagonal barium ferrites

M-type hexagonal barium ferrite (BaM) has received much attention in the application of self-biased microwave devices because of its large anisotropic field (Ha) and high saturation magnetization (Ms), but the increased Ha inevitably increases the microwave magnetic loss of the device. In addition, the devices need to have a high Ms for high frequency applications. To address these issues, we used La3+ and Zn2+ instead of Ba2+ and Fe3+ ions to modulate the Ha and Ms of BaM, respectively. Ba1-yLayFe12-xZnxO19 (x=y=0.1–0.5) M-type hexagonal ferrite was synthesised by conventional solid-phase methods. The La-Zn co-substituted BaM samples were shown to be purely single phase by X-ray diffraction (XRD) analysis. The lattice parameters, specific surface area, crystallite size, dislocation density and microstrain of the samples were also calculated using the XRD data. Furthermore, La3+ and Zn2+ can not only modulate the sample Ha and Ms between 10,214–12,102 Oe and 62.94–78.23 emu/g, respectively, while making the sample more denser. At x=0.3 BaM detects relatively satisfactory properties: large Ms=63.12 emu/g, suitable Ha=10,214 Oe and Hc=2248.87 Oe, high Mr/Ms=0.832 and narrow ferromagnetic resonance linewidth (= 903 Oe), which provide good candidates for next-generation self-biased and low-loss microwave wave devices.

Strong and ductile high temperature soft magnets through Widmanstätten precipitates

Fast growth of sustainable energy production requires massive electrification of transport, industry and households, with electrical motors as key components. These need soft magnets with high saturation magnetization, mechanical strength, and thermal stability to operate efficiently and safely. Reconciling these properties in one material is challenging because thermally-stable microstructures for strength increase conflict with magnetic performance. Here, we present a material concept that combines thermal stability, soft magnetic response, and high mechanical strength. The strong and ductile soft ferromagnet is realized as a multicomponent alloy in which precipitates with a large aspect ratio form a Widmanstätten pattern. The material shows excellent magnetic and mechanical properties at high temperatures while the reference alloy with identical composition devoid of precipitates significantly loses its magnetization and strength at identical temperatures. The work provides a new avenue to develop soft magnets for high-temperature applications, enabling efficient use of sustainable electrical energy under harsh operating conditions.

Development of Soft Magnetics Fe-B-C-Si Amorphous Alloys with High Magnetization and Sufficient Amorphous-Forming Ability

The amorphous-forming ability (AFA) and the magnetic properties of the amorphous Fe-B-C-Si soft magnetic alloys have been investigated. Though the ternary Fe-B-C alloys exhibit high magnetization, their AFA is poor, which has prevented their practical application. It was confirmed that the addition of Si to the Fe-B-C alloys significantly improves AFA. Furthermore, it has been found that the composition range of the Fe-B-C-Si alloys with sufficient AFA can be identified by focusing on the enthalpy of mixing (ΔHmix) and δ, which is related to the ratio of atomic radius between the constituent elements, of the alloys. The Fe-B-C-Si amorphous alloys that combine the high saturation magnetization of 175−177 A m2/kg with sufficient AFA to produce thick sheets whose thickness of 70 μm or more have been successfully developed by using the relationship between ΔHmix, δ and AFA as a guideline. The Fe-B-C-Si amorphous alloys are expected to be applied to core materials for various magnetic components.

Enhancing Surface Properties of Cu-Fe-Cr Alloys through Laser Cladding: The Role of Mo and B4C Additives

Laser cladding is a powerful surface treatment technique that can significantly enhance the properties of metal alloys. This study delves into the liquid phase separation behavior of Cu-Fe-Cr alloys under the rapid solidification conditions inherent in laser cladding and evaluates the influence of 4% Mo and 2% B4C additions on the resulting alloy characteristics. The intensive undercooling characteristic of the laser cladding process facilitates the alloy’s entry into the liquid-phase immiscibility gap, prompting pronounced phase separation. Our investigation reveals the emergence of Fe-rich regions, exhibiting a variety of shapes, set against a continuous Cu-rich matrix. The incorporation of Mo and B4C was found to modulate the mixing enthalpy and entropy, thereby refining the phase distribution: Mo was observed to prevent the agglomeration of Fe cores, resulting in a dispersion of isolated Fe cores throughout the Cu-rich matrix, while B4C promoted a more uniform compositional distribution. This study further enumerates the enhancements in microhardness, wear resistance, and magnetic properties of the alloys. Notably, the Cu-Fe-Cr-Mo-B4C alloy demonstrated a microhardness exceeding 600 HV, a low coefficient of friction around 0.15, high saturation magnetization, and reduced coercivity. These results underscore the efficacy of laser cladding in tailoring the microstructure and properties of Cu-Fe alloys, providing insights for the controlled manipulation of phase separation to optimize surface characteristics for engineering applications.