Saturation Magnetization Ms Research Articles

Effect of nickel doping on magnetic and dielectric properties of orthorhombic calcium ferrite nanoparticles

Nickel (10∼50 mol%) doped calcium ferrite nanoparticles (NPs) are synthesized by the solution combustion method using lemon juice extract as a reducing agent, followed by calcination at 500°C. The calcined samples are characterized with different techniques. The Bragg reflections of Nickel doping confirm the formation of a single orthorhombic calcium ferrite phase. The crystallite size is estimated using both Scherrer's and the W-H plot method. The surface morphology consists of irregular size and shaped agglomerated NPs along with pores and voids. A blueshift and a broad absorption spectrum is observed with an increase in the direct energy band gap. The direct energy band gap estimated from Wood and Tauc's relationship was found to be 2.91∼2.97 eV with an increase in dopant concentration. The magnetic analysis provided values for saturation magnetization (Ms), remanence (Mr), and coercivity (Hc), while dielectric studies demonstrated a dielectric constant of 2.81, 2.14, and 1.67 with increasing dopant concentration. The variation of dielectric properties of the sample as a function of frequency in the range 0.1∼20 MHz has been studied at room temperature. The dielectric properties of CaFe2O4: Ni (1∼9 mol%) NPs clearly indicate that there is a more pronounced dispersion at lower frequencies, gradually reaching saturation as the frequency increases. The dielectric loss was found to decrease from 4.62, 3.22, and 2.32 with an increase in Ni2+ substitution (10, 30, and 50 mol%) respectively. These results indicate the suitability of these samples for applications in memory devices and high-frequency applications.

Chemical synthesis of Mn–Zn magnetic ferrite nanoparticles: Effect of secondary phase on extrinsic magnetic properties of Mn–Zn ferrite nanoparticles

This paper presents a comprehensive investigation of the magnetic properties of co-precipitated MnxZn1–xFe2O4 nanoferrites, where x takes the values of 0.5, 0.6, and 0.7. X-ray diffraction patterns indicated the presence of spinel phase. However, the ferrite composition x = 0.6 contains little trace of secondary phase α-Fe2O3. The occurrence of cation redistribution in the current ferrite samples can be concluded from the deviation of oxygen position parameter (U) to that of optimum value (0.375). The bond angles facilitate the reduction of the A–B interaction and the increase of the B–B interaction. With the substitution of Mn2+ ions, the saturation magnetization (Ms) exhibits both drops and increases whereas the coercivity (Hc) consistently declines. The ferrite composition x = 0.7 exhibits the maximum value of Ms and is equal to 27.9 emu/g. The blocking temperature (TB) rises in proportion to the degree of Mn2+ ion doping. The observation of quadruple doublets in the Mӧssbauer spectra indicates that the ferrite nanoparticles exist in single domain state exhibiting the quadruple interactions. The range of isomer shift (δ) 0.199–0.267 mm/s indicates the existence of exclusively high spin Fe3+ ions. Two paramagnetic doublets are anticipated to exist as a result of the core and shell of present ferrite nanoparticles. In the core-shell morphology of nanoparticles, the core is characterized by larger quadruple splitting (Δ) while the shell is characterized by smaller Δ. The results are integrated in terms of magnetocrystalline anisotropy and secondary phase presuming the core-shell structure of nanoparticles.

Acoustic shock wave processing on amorphous carbon quantum dots – correlation between spectroscopic-morphological–magnetic and electrical conductivity properties

In this context, we report the acoustic shock wave processing on amorphous Carbon quantum dots (a-CQD) such that its degree of graphitization and magnetic properties are analyzed. Analytical techniques such as the Raman spectrometer, high resonation–transmission electron microscopy (HR-TEM) and vibrating sample magnetometer (VSM) are utilized to understand the structural, morphological and magnetic properties changes under shocked conditions. The Raman spectroscopic data reveal that the ID/IG ratio is slightly reduced under shocked conditions and the observed values are 0.78, 0.77 and 0.75 for the respective 0, 150 and 300 shocked conditions. The formation of ultra-short-range graphitic nanostructures is confirmed by HR-TEM results at the 300-shocked condition. The most convincing and supporting results for the enhancement of the degree of graphitization are found by the outcome of the magnetic properties such that the saturation magnetization (Ms) is found to be linearly reduced with respect to the number of shock pulses and the observed values are 0.869, 0.757 and 0.710 emu/g for the 0, 150 and 300 shocked conditions, respectively. The electrical resistance of the a-CQD is found to be linearly reduced with respect to the number of shock pulses due to the reduction of sp3 carbon networks. The formation of crystalline graphitic nanostructures in amorphous CQD is explained on the basis of the hot-spot nucleation mechanism. Based on the obtained Raman, HR-TEM and VSM results, during the shocked conditions, slight enhancement of the graphitization is observed; however, from the structural stability point of view, the Carbon dots have high shock resistance than that of the amorphous carbon nanoparticles, multi-wall carbon nanotubes, and reduced graphene oxide nanoparticles. Hence, the title quantum dots can be strongly considered for the applications of device fabrication.

On the correlation between mechanical, optical, and magnetic properties of co-substituted Sn1-x-yZnxMyOz metal-oxide ceramics with M = Fe, Co, Ni, and Mn

We report here the FTIR, optical, and magnetic properties of Sn1-x-yZnxMyOz ceramics with various x, y, and M. The pure samples are called S1, S2, and S3 for ZnO, SnO2, and SnZn. The co-substituted samples are called S4, S5, S6, and S7 for SnZnFe, SnZnCo, SnZnNi, and SnZnMn, with Zn = 0.50, Sn = 0.25, and M = 0.25. The Young's modulus, was decreased from 5.70 (D/cm2) for S3 to 4.59, 3.14, 2.59, and 3.05 (D/cm2) for S4, S5, S6, and S7. The Eg was decreased from 2.13 eV for S3 to 2.16, 2,2, and 1.6 eV for S4, S5, S6, and S7. The pure samples (S1–S3) exhibit ferromagnetic behavior at 300 K, and combination of paramagnetic and ferromagnetic behaviors at 10K. In contrast, the samples (S4–S7) exhibit a combination of paramagnetic and ferromagnetic behaviours at both temperatures. The Curie temperature (Tc) obtained through zero-field cooling (ZFC) and field cooling (FC) is close to 300 K for S1–S3, S5, S6, 200 K for S4, and 20 K for S7. The real saturated magnetization (Ms) of the ZnO sample was decreased by the addition of SnO2, and then increased by the addition of Mn, Ni, Fe, and Co sequentially. Ms was increased from 12.31 (emu/g) for S3 at 300 to 16.24, 31.04, 27.27, and 10.49 (emu/g) for S4, S5, S6, and S7, and from 16 (emu/g) to 87, 730, 83, and 29 at 10 K. Remnant magnetization (Mr) decreases with the addition of SnO2 to ZnO and is not affected by the addition of TMs, just in the case of Co, where it increases. The coercive field decreases, but the switching field increases markedly with the addition of Mn and Ni, transforming the system from a hard magnetization to a soft magnetization system.

Enhanced Magnetic Properties of Gd-Doped ZnO by Varying the Gd Concentration via Co-Sputtering Technique

This study reports on the effect of Gd concentrations on the properties of Gd-doped ZnO films. The films were prepared using co-sputtering method at room temperature. Characterization tools such as X-ray diffraction (XRD), atomic force microscopy (AFM), and vibrating sample magnetometer (VSM) were used to analyze the properties of the prepared films. XRD results observed that all the films are well crystalline and designated to the hexagonal wurtzite structure of ZnO with no secondary phases, which confirmed the successful of doping the Gd into ZnO. Topography analysis from AFM discovered the increase of Gd concentrations of Gd-doped ZnO films leads to the increase in grain size and rougher surface of the films. The magnetization of the films effectively depends on the Gd concentrations, which the diamagnetic behavior changed to ferromagnetic behavior upon Gd doping. A film with higher Gd doping concentration is more effective than lower Gd doping in terms of saturation magnetization (Ms), coercivity (Hc) and remanent magnetization (Mr). These findings revealed that optimizing the Gd concentration is very crucial in enhancing the magnetic properties of Gd-doped ZnO films.

Properties and antibacterial activity of MnFe2O4 nanoparticles obtained by pulsed laser ablation in liquid

In this study, MnFe2O4 nanoparticles (NPs) were fabricated via pulsed laser ablation in liquid. Chemical and structural composition, microstructure, magnetic and antibacterial properties were characterized. Spinel was found as the main crystalline phase, while Fe2O3 and Mn2O3 were observed as the major secondary phases, all identified by X-ray diffractometry (XRD). Observation by Transmission Electron Microscopy (TEM) indicated that most of the nanoparticles were spherical in shape and found in agglomerates, most likely because of their magnetic nature. Moreover, Fast Fourier Transform of selective area electron diffraction patterns pointed at the existence of crystalline particles. The coercive field (Hc) and saturation magnetization (Ms) values determined for these NPs were found to increase with decreasing temperature. Their antibacterial properties were evaluated using the viable bacteria counting technique (colony) for MnFe2O4 concentrations of 100 and 300 μg/mL with Bacillus subtilis, Salmonella typhimurium, Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli strains.

Forces driving ecological degradation in southern China during the MIS3: Natural or anthropogenic?

The role of natural forces in ecological degradation remains controversial owing to the scarcity of records of past land cover destruction with no or less anthropogenic disturbance. Here, we reconstructed land cover changes during the Marine Isotope Stage 3 (MIS3) in the Nanling Mountains in southern China using the δ13C and saturation magnetisation (Ms) records of a speleothem from Zuixian Cave. The persistently positive δ13C values since 51.9 ka B.P. suggest vegetation reduction and karst rocky desertification in the Nanling Mountains. This prolonged ecological degradation was exposed to reduced precipitation, weak pedogenesis (as indicated by less depleted δ18O ratios and low Ms values), and recurring forest fires. Our results highlight the critical role of natural forces in ecosystem degradation, challenging the view of human domination on environmental change. These findings could improve our understanding of the drivers of current ecological evolution and global change.

The role of Sn and Zn substitutions on the magnetic properties of nanosized Y-type hexaferrite prepared by sol-gel auto-combustion method

The current paper has focused on the improvement of the magnetic performance of the Sn, Zn-doped Y-type hexaferrite nanoparticles via the sol–gel auto-combustion method. The partial replacement of nonmagnetic Zn2+ and Sn4+ cations for the magnetic Fe3+ cation was studied. At the low Zn-Sn concentration, the Sn4+ cations had a preference for octahedral locations (12k, 2a, 4f2) and the Zn2+ cations had a strong tendency to move to the tetrahedral spaces (4f1), respectively. Based on this data, the single-phase hexaferrites with the chemical formula of Sr2Co1.7Mg0.3Fe(12-x)Snx/2Znx/2O22 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were successfully synthesized via the sol–gel auto-combustion method. The x-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Thermal Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA), Field Emission Scanning Electron Microscopy (FESEM) and Vibrating Sample Magnetometer (VSM) were carried out to investigate the obtained ferrite performance. The results revealed the formation of the single-phase platelet-like Y-type hexagonal ferrites after calcinations at 1000 °C with a thickness of 30–70 nm and a particle size of 90–210 nm. The obtained nanosized ferrites had the magnetic coercivity (Hc) and the saturation magnetization (Ms) in the range of 2100–637 Oe and 38–48 emu g−1, respectively. The addition of Sn, Zn dopants enhanced the saturation magnetization and reduced the magnetic coercivity, which can make this ferrite a candidate for some applications.

Tuning the Physical Properties of Ag and ZnO Nanoparticles to be Applied in Various Applications

Silver nanoparticles (Ag-NPs) accompanied by zincite (ZnO) and hematite (Fe2O3) (Ag-Z-H) at different annealing temperatures (as dried, 400°C) were prepared using the Flash auto-combustion method. X-ray diffraction pattern assured the cubic structure of Ag-NPs for both samples. The morphology using atomic force microscopy assured the formation of nanoparticles with small agglomeration. By increasing the annealing temperature, the crystallite and particle sizes increased. Moreover, Fourier transforms infrared analysis assured the bond formation of the nanoparticles. The magnetic measurement indicated the increase of the coercivity (Hc) of (Ag-Z-H) nanoparticles at 400°C by nine-fold compared with the as-dried sample. Contrarily, the as-dried (Ag-Z-H) nanoparticles showed 1.8-fold larger saturation magnetization (Ms) than at 400°C. The high-frequency application was studied from the magnetic measurement and showed that both samples could be applied in the ultra-high frequency microwave region in the P band. As a result of the antimicrobial study, (Ag-Z-H) nanoparticles at 400°C showed stronger antimicrobial activities than the as-dried sample. Thus, the strong recommendation of as-dried (Ag-Z-H) nanoparticles at 400°C could be used as an effective alternative antibacterial drug, especially (Ag-Z-H) nanoparticles at 400°C.

Effect of Ag-doping process into the yttrium iron garnet (Y3Fe5O12) thin films on the structural, magnetic and optical properties

In this work, the effect of Ag doping process (directly and as a nanoparticle) into the Y3Fe5O12 (YIG) thin films on the structural, morphological, optical and magnetic properties was studied in detail. Ag-doped YIG thin films were grown on thermally oxidized Si substrates by following sol–gel and spin-coating methods. All films were crystallized without cracks by two-stages heat treatment process. The XRD patterns confirm the formation of YIG peaks, and metallic Ag peaks which settled into the structure without bonding with the YIG components. In both Ag doping processes, the coercive field (Hc) and saturation magnetization (Ms) values of the samples containing 3% Ag are significantly lower than the other samples. The Ms values of 5% Ag doped samples were found the highest in both series. The Ms values of the films between in-plane and out-of-plane measurement increased with the Ag concentration. The optical measurements indicate an absorption peak in the range of 0–4 eV in both sample series and the optical band gap of the films decreased with the Ag doping due to its metallic characteristic. The ferromagnetic resonance measurements indicate that the lowest FMR linewidth as 92 Oe is seen in the 1% Ag-doped YIG sample. The relatively cheap and easy production of the used method and additive material may enable the widespread the usage of Ag-doped YIG thin films in magneto-optical devices.

Structural, thermal, magnetic and microwave-absorbing properties of spinel-structured high entropy oxide (MnFeCoNiX)3O4 (X = Zn, Cu, Cr)

Within the present work, a series of spinel-structured (MnFeCoNiX)3O4 (X = Zn, Cu, Cr) high entropy oxides (HEOs) were fabricated by co-precipitation method and the subsequent heat treatment. The phase composition, microstructure, thermal stability, magnetic property and electromagnetic (EM) wave loss ability were comprehensively studied. It is found that spinel-structural (MnFeCoNiX)3O4 HEOs are well-crystallized at above 800 °C with a space group Fd-3m. Morphological analysis reveals that grains of different HEOs contain nano-domains with particle sizes between 100 nm and 500 nm. In addition, Mn, Ni, Co, Fe, Zn, Cr and Cu elements are homogeneously distributed and the chemical states of Mn, Ni, Co and Fe are all +2 and + 3, while Cu only exists in +2 state. Thermal stability analysis shows that (MnFeCoNiCu)3O4 HEO is able to keep stable at 1000 °C. Moreover, the (MnFeCoNiCu)3O4 sample exhibits the best magnetic properties and EM microwave loss ability in comparison with (MnFeCoNiZn)3O4 and (MnFeCoNiCr)3O4. For (MnFeCoNiCu)3O4, the values of saturation magnetization (Ms) and coercivity (Hc) are 38.6 emu/g and 52.6 Oe, respectively. Meanwhile, (MnFeCoNiCu)3O4 displays a minimum reflection loss (RL) of −15.5 dB at 8.48 GHz with a thickness of 4.5 mm and a wide effective absorption bandwidth (EAB) of 8.84 GHz with the sample thickness of 5 mm. It is expected that the excellent high-temperature stability and good EM wave absorbing performance of high entropy (MnFeCoNiCu)3O4 could make it potentially useful in EM wave absorption under elevated temperatures.

Bifunctional of Fe3O4@chitosan nanocomposite as a clarifying agent and cationic flocculant on different sugar solutions as a comprehensive semi industrial application

In the sugar industry, eliminating side impurities throughout the manufacturing process is the most significant obstacle to clarifying sugar solutions. Herein, magnetic chitosan (MCS) nanocomposite was Fabricated to be used as a biodegradable, environmentally friendly clarifying agent throughout the cane juice and sugar refining processes. Fe3O4 was synthesized using the coprecipitation procedure, and then MCS was combined using a cross-linking agent. Furthermore, 14.76 emu g−1 was the maximum saturation magnetization (Ms) value. Because MCS is magnetically saturated, it may be possible to employ an external magnetic field to separate the contaminant deposited on its surface. Additionally, zeta potential analysis showed outstanding findings for MCS with a maximum value of (+) 20.7 mV, with improvement in color removal % up to 44.8% using MCS with more than 24% in color removal % compared to the traditional clarification process. Moreover, utilizing MCS reduced turbidity from 167 to 1 IU. Overall, we determined that MCS nanocomposite exhibits considerable effectiveness in the clarifying process for different sugar solutions, performing as an eco-friendly bio-sorbent and flocculating material.

Improved Anti-Saturation Performance of Fe-Si-Al Soft Magnetic Powder Core via Adjusting the Alloy Composition

Ball-milled Fe-Si-Al soft magnetic powder cores with the particle compositions away from the classical Sendust point were prepared in this work. The influences of alloy composition on the metallographic structure, density, hardness, and resistivity of Fe-Si-Al alloy, as well as the frequency-dependent permeability, loss, and the anti-saturation performance of Fe-Si-Al powder cores, were investigated systematically. It was found that the hardness of Fe-Si-Al alloy increases with the Si mass ratio and the saturation magnetization (Ms) increases with the Fe mass ratio. The alloy hardness affects the particle size after the ball-milling process and, thus, influences the porosity of the powder core. Together with adjusting the demagnetization field by controlling the particle size and the core’s porosity, changing the alloy composition to drive K and λ deviating from zero can effectively improve the anti-saturation performance of Fe-Si-Al powder cores at the expense of hysteresis loss, to some extent. In this work, good comprehensive magnetic properties were obtained in the Fe85.5-Si12-Al2.5 powder core. Its effective permeability percentage at 100 Oe and Ms were 59.12% and 132.23 emu/g, respectively, which are higher than those of the classical Sendust core. This work provides a feasible idea for optimizing the overall performance of the high-power magnetic device.

Magneto-Mechanical Coupling Study of Magnetorheological Elastomer Thin Films for Sensitivity Enhancement.

Magnetorheological elastomer thin films (MREFs) exhibit remarkable deformability and an adjustable modulus under magnetic fields, rendering them promising in fields such as robotics, flexible sensors, and biomedical engineering. Here, we fabricated MREF by introducing magnetostrictive particles (MSPs) and evaluated the magneto-mechanical coupling effect on the enhancement of sensitivity. The saturation magnetization (Ms) in a parallel anisotropic TbDyFe-PDMS MREF was 5.8 emu/g, and the initial tensile modulus was 55% greater than that of an Iso MREF. We propose a nonlinear magnetorheological formula on the magnetostriction effect, incorporating magnetic dipole interactions and the nonlinear prestress of magnetic particles. This formula highlights the complex nonlinear relationship between the external magnetic field (H) and the key parameters that affect the enhanced MR effect of MSPs-MREF, such as saturation magnetization, remanence (Mr), magnetostriction constant (λs) and stress deviator in ferromagnetic particles (Sed) in the magnetic chain structure. Furthermore, we validate the influence of the key parameters of the rectified magnetorheological formula on a nonlinear magneto-mechanical behavior of MSPs-MREF in PDMS-based MSPs-MREF models by using finite-element simulations. Finally, we developed a biosensor based on MSPs-MREF to detect human serum albumin at low concentrations in human urine samples. There is a 4-fold increase in sensitivity, a lower detection of limit (0.442 μg/mL), and a faster response time (15 min) than traditional biosensors, which in the future might provide an effective way of detecting biomolecules of low concentrations.

ZnO-Cu/NiFe2O4 magnetic nanocomposite with boosted photocatalytic and antibacterial activity against E. coli.

A novel ZnO-Cu/NiFe2O4 hybrid nanocomposite with increased photocatalytic and antibacterial activities was synthesized by solid-state mixing of NiFe2O4 with Cu-doped ZnO (ZnO-Cu) and subsequent thermal processing. Various characterization techniques, like X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL), Raman spectroscopy, vibrating-sample magnetometry (VSM) and Brunauer-Emmett-Teller (BET) analysis, have been used to study and characterize the synthesized nanomaterial. The XRD results demonstrated a hexagonal wurtzite phase of the ZnO nanoparticles and a reduction in the average crystallite size with doping and composite formation. The average crystallite size was found to be 32.36 ± 0.25 nm for ZnO, 29.87 ± 0.28 nm for ZnO-Cu and 24.73 ± 0.21 nm for the ZnO-Cu/NiFe2O4 nanocomposite. FESEM analysis revealed that the synthesized nanoparticles possess a nearly spherical morphology and average particle sizes of about 89 ± 1.8, 78 ± 1.9 and 63 ± 1.6 nm for the ZnO, ZnO-Cu and ZnO-Cu/NiFe2O4 samples, respectively. ZnO and ZnO-Cu/NiFe2O4 nanocomposite exhibit specific surface area of 6.67 and 12.38 m2/g, respectively, as observed from BET analysis. FTIR analysis indicated the enhancement of carboxylate and hydroxyl groups with doping and nanocomposite formation. The retentivity (Mr ∼ 0.243 emu/g), coercivity (Hc∼ 98.1 Oe) and saturation magnetization (Ms∼ 3.048 emu/g) values of the ZnO-Cu/NiFe2O4 nanocomposite, obtained from VSM analysis, confirm its superparamagnetic characteristics. To comprehend the photocatalytic activity of the prepared nanocomposite, dye degradation was also investigated. Here, we have shown that the ZnO-Cu/NiFe2O4 nanocomposite is capable of achieving the highest photocatalytic activity of 94.2% compared to ZnO (56.2%) and ZnO-Cu (86.4%). The antibacterial activity on Escherichia coli (E. coli) was investigated and the observed zones of inhibition for ZnO, ZnO-Cu and the ZnO-Cu/NiFe2O4 nanocomposite were 20.1 ± 0.21, 20.9 ± 0.20 and 27.3 ± 0.24 mm, respectively. Assuming the antibacterial activity of control ampicillin as 100%, the ZnO-Cu/NiFe2O4 nanocomposite has shown the maximum antibacterial activity of 107.5 ± 0.94% as compared to the other samples. According to our observations, the ZnO-Cu/NiFe2O4 hybrid nanocomposite exhibits the highest level of inhibition among all the samples and has the potential to be used in various environmental, biological and industrial applications.

Manipulating the Curie point in γ-Fe filled carbon nano-onions: The role of Mn and Gd for enhanced magnetic functionalities

Recent works have proposed the stabilization of γ-Fe nanocrystals inside carbon nano-onions (CNOs) and nanotubes (CNTs) as active ferromagnetic phases for possible applications in hyperthermic dissipative systems. Stabilization of the γ-phase of iron is of particular interest due to the unit-cell dependent ferromagnetic properties and controllable Curie point. Here we investigate a modification of the chemical vapor synthesis (CVS) method for the in-situ manipulation of γ-Fe nanocrystals within CNOs, in presence of bis(isopropyl-cyclopentadienyl)manganese or tris(tetramethyl-cyclopentadienyl)gadolinium(III) as additional growth-precursors. In the presented experiments ferrocene, dichlorobenzene and sulfur mixtures were employed with a fixed ratio. Interestingly, when employing bis(isopropyl-cyclopentadienyl)manganese we demonstrate the stabilization of a modified FCC γ-Fe phase inside the CNOs, identifiable as a γ-Fe23C6 through X-ray diffraction and refinement of the structural model (obtained by employing the Rietveld method), with unit cell parameters a=b=c= 10.5569 Å and space group Fm-3m. The relative amount of Mn content was found to vary from 0.2% to 0.5%. Differently, comparative experiments performed in presence of great excess of tris(tetramethylcyclo-pentadienyl)gadolinium(III) reveal a significant variation of the sample’s morphology, with the nucleation of Gd nanoparticles around γ-Fe filled CNOs. Magnetic characterization with field-dependent zero field cooled (ZFC) and field cooled (FC) acquisitions revealed for the first batch of experiments (method 1) a ferromagnetic behavior comparable to that of γ-Fe, with a T1 Curie point located in proximity of T∼ 400 K and a T2 Curie point in proximity of T∼90 K. Differently, for method-2, an important interplay of ferromagnetic and paramagnetic components was found in the Gd-decorated γ-Fe filled CNOs, with a reduction of the Curie point down to T∼350 K. The presented findings highlight the important role of 1) the γ-Fe23C6 phase in enhancing the saturation magnetization Ms of the filled CNOs and 2) the crystallinity of the Gd-component in allowing for an enhancement of the paramagnetic response in the filled CNOs.

Effect of coercive aluminium on the structural and magnetic characteristics of calcium and magnesium based hexaferrites

Aluminum substituted Calcium-Magnesium (Ca-Mg) hexaferrites having general formula Ca0.5Mg0.5Fe12-xAlxO19 (where x is increased with increment of 0.5 from 0.0 to 2.0) are prepared by sol–gel auto combustion technique. X-ray diffraction patterns confirm the hexagonal structure with no evidence of secondary phases. The reduction in lattice parameters is observed as the Al+3 doping level increases. This can be attributed to the short ionic radii of Al+3 ions (0.535 Å) compared to Fe+3 ions (0.645 Å). The obtained c/a ratio falls within the acceptable range of 3.98. Consequently, the formation of magnetoplumbite structure is also confirmed. The SEM image reveals the uniform distribution of particles. The exchange of Fe+3 ions with coercive Al+3 ions led to a decline in saturation magnetization Ms and a significant increase in the coercivity Hc. The magnetic moment mB and Mr of hexaferrites exhibit a decline when Al ions are introduced. This reduction can be ascribed to several factors: the substitution of non-magnetic Al3+ ions in place of Fe3+ ions, the spin-canted ordering of Fe3+ ions, and the valency of Fe ions from 3+ to 2+.

Orange peel magnetic activated carbon for removal of acid orange 7 dye from water

Magnetic activated carbon resources with a remarkably high specific surface area have been successfully synthesized using orange peels as the precursor and ZnCl2 as the activating agent. The impregnation ratio was set at 0.5, while the pyrolysis temperature spanned from 700 to 900 °C. This comprehensive study delved into the influence of activation temperatures on the resultant pore morphology and specific surface area. Optimal conditions were discerned, leading to a magnetic activated carbon material exhibiting an impressive specific surface area at 700 °C. The Brunauer–Emmett–Teller surface area reached 155.09 m2/g, accompanied by a total pore volume of 0.1768 cm3/g, and a mean pore diameter of 4.5604 nm. The material displayed noteworthy properties, with saturation magnetization (Ms) reaching 17.28 emu/g, remanence (Mr) at 0.29 emu/g, and coercivity (Hc) of 13.71 G. Additionally, the composite demonstrated super-paramagnetic behaviour at room temperature, facilitating its rapid collection within 5 s through an external magnetic field. Factors such as absorbent dose, initial concentration of the adsorbate, contact time, and pH were systematically examined. The adsorption behaviour for acid orange 7 (AO7) was found to adhere to the Temkin isotherm models (R2 = 0.997). The Langmuir isotherm model suggested a monolayer adsorption, and the calculated maximum monolayer capacity (Qm) was 357.14 mg/g, derived from the linear solvation of the Langmuir model using 0.75 g/L as an adsorbent dose and 150–500 mg/L as AO7 dye concentrations. The pseudo-second order model proved to be the best fit for the experimental data of AO7 dye adsorption, with a high coefficient of determination (R2) ranging from 0.999 to 1.000, outperforming other kinetic models.

Magnetism of metastable γ-Fe85Pd15 nanowire arrays across an unusually broad temperature range (5 K to 800 K).

Arrays of 50 nm diameter Fe85Pd15 cylindrical nanowires were electrochemically grown, crystallizing in a metastable γ-Fe(Pd) fcc A1 disordered solid solution. After performing a heating-cooling thermal cycle between 300 K and 1000 K, the γ-Fe(Pd) fcc metastable phase still predominates (97%), coexisting with a not-fully-identified minority phase. The thermal cycling induces a moderate increase in the crystallite size and a reduction of the lattice parameter although leading to a significant heating-cooling magnetic hysteresis. No further changes in temperature-dependent magnetization, M(T), are observed during subsequent cycling. The full-range (5 K to 800 K) saturation magnetization Ms(T) curve is quite accurately described by a phenomenological expression, which provides a Bloch-type contribution as T → 0 and undergoes the critical behavior near the Curie temperature TC. An upturn in Ms(T) is observed below 100 K which is described by a spin-glass-like second contribution, with freezing temperature Tf = (80 ± 2) K, and kBTf comparable to the exchange interactions in Fe-Pd systems. A Curie temperature of TC = 830 K, and a critical exponent value β = 0.42 ± 0.05 are estimated. These regimes (below and above 100 K) are also observed in the magnetization process. The temperature dependence of coercivity between 100 K and 800 K is consistent with a nucleation/propagation remagnetization mechanism, with activation energy of (320 ± 20) kJ mol-1 and critical field for magnetization reversal of (65 ± 1) mT, at 0 K. The analysis of the effective magnetic anisotropy as a function of temperature allows us to conclude that it essentially arises from the balance between different magnetostatic contributions.

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.