Variation Of Coercivity Research Articles

Multiferroic properties of NiFe2O4-Ba0.7Ca0.3TiO3 nanocomposites

In this report, we present results on the multiferroic properties of four nanocomposite samples of NiFe2O4-Ba0.7Ca0.3TiO3 (NFO/BCTO), which were fabricated through combinations of high-energy ball milling, heat treatment, and spark plasma sintering techniques. Structural analyses revealed that these samples simultaneously contain two phases of nano-sized NiFe2O4 (NFO) and Ba0.7Ca0.3TiO3 (BCTO) crystals. The addition of NFO into the BCTO-host did not alter the crystal structure but significantly improved the multiferroic characteristics compared to pure BCTO. Furthermore, variations in saturation magnetization (M s) and coercivity (H c) were investigated as a function of temperature. The results showed that Ms increased gradually with the concentration of NFO. In terms of temperature dependence, M s(T) data deviated from the Bloch’s law with an exponent coefficient α changing in the range of 1.8–1.9, decreasing gradually as the NFO concentration increased. Meanwhile, H c decreased gradually as the NFO concentration increased and followed the Kneller’s law in terms of temperature dependence.

Structural properties controlled magnetisation of Ni/Al multilayers sputtered on flexible polymer substrate: Impact of Ni deposition rates

The goal of this work is to determine how the rate of Ni deposition rates affect the structural characteristics that regulate the magnetization of Ni/Al multilayer thin films sputtered on flexible acrylic acetate polymer substrates. The films with a 5[Ni(20 nm)/Al(10 nm)] structure were gradually sputtered as different Ni deposition rates in the total thickness of 150 nm. With an increase in the rate of Ni deposition, the Ni contents increased from 61.5% to 69.6%. And, X-ray diffraction analysis verified that the films featured a face-centered cubic structure with variable peak intensities. Also, the scanning electron microscopy surface morphology analyses revealed that variations in the film surfaces were a result of the deposition rates. For magnetic measurements, the differences in the structural analysis were observed to cause a notable variation in saturation magnetization, MS, and coercivity, HC values. Accordingly, MS values increased consistently between 359.0 and 389.7 emu cm−3, but HC values decreased from around 34–32 to 28 Oe with the increase in Ni deposition rate from 0.02 to 0.10 nm s−1. It is also observed that when the Ni layers are generated at very fast deposition rates, the Ni/Al multilayer films have a high MS/HC ratio, which is significant for magnetic sensors. It has been concluded that the magnetisation of Ni/Al multilayer thin films can be controlled by the structural properties adjusting the Ni deposition rate.

Comparative Study of Rare Earth Nd and Sm Doping on the Structural, Morphological, Optical, Magnetic, and Electromagnetic Traits of Mg-Zn-Cu Spinel Nanoferrites

In the current study, the magnetic nanoparticles of neodymium and samarium substituted Mg-Zn-Cu, with a chemical composition of Mg0.5Zn0.5Cu0.05RxFe1.95-xO4 (x = 0.05; R = Nd, Sm) were produced via the sol-gel auto-combustion route. XRD indicates the evolution of a cubic symmetry having Fd3m space group and no impurities at the room temperature. The FESEM images show the irregularly shaped and agglomerated grains in all samples. FTIR examination reveals the stretching vibrations among the metal cations and anions at interstitial vacancies. The M-H graphs demonstrates that the prepared nanoferrites have low rentivity (0.18–0.84 emu g−1) and coercivity (11.25–34.03 Oe) indicating the formation of superparamagnetic nature. From the electromagnetic traits, the observed sample’s real magnetic permeability (μ″) and permittivity (ε′) along with dielectric loss and magnetic loss reduced with increasing applied field frequency, indicating the typical behaviour of spinel nanoferrites. This may be explained by Maxwell-Wagner interfacial polarisation and the electron hopping among the ferrous and ferric ions. The variations in coercivity, anisotropy constant, and electromagnetic traits provide strong evidence that all of the samples are thermally stable and have the potential to be used in solenoids and transformers, and also, in the more resistive devices that operate at the high frequency.

Signatures of nearly compensated magnetism and spin glass behavior in highly frustrated β-Mn-type Mn50Fe25+xAl25-x Heusler alloys.

The present study examines the effect of Fe/Al concentration on the structural and magnetic properties of Mn-rich Mn50Fe25+xAl25-x (x = 5, 10, 15) Heusler alloys through x-ray diffraction, temperature- and field-dependent DC magnetization, thermoremanent magnetization, magnetic memory effect, AC susceptibility measurements, and DFT calculations. The samples crystallize in a cubic β-Mn structure. The trend shows a reduction in lattice parameters (unit cell volume) with the increasing Fe proportion. These alloys exhibit strong antiferromagnetic interactions with large frustration parameters, indicating the presence of competing magnetic interactions. The DC magnetization data reveal spin glass-like features with a peak at spin glass freezing temperature (Tf). The observation of bifurcation in temperature-dependent zero-field-cooled and field-cooled magnetization curves, exponential dependence of the temperature variation of remanence and coercivity, magnetic relaxation, and magnetic memory effect below Tf support the spin-glass character of these alloys. The frequency dependence of Tf is also examined in the context of dynamic scaling laws, such as the Vogel-Fulcher law and critical slowing down model, which further supports the presence of spin glass behavior. In the theoretical DFT calculations, the electronic structure is found to be metallic and similar for both spin projections. Moreover, the antiferromagnetic arrangement of the magnetic moments, in line with the experimental observations, is stabilized by exchange interactions, resulting in an almost compensated total magnetic moment of 0.02-0.38µB/f.u. This is probably caused by the frustrated structure and non-stoichiometric compositions of Mn50Fe25+xAl25-x.

Preparation and analysis of Mn1-xZnxFe2O4 nanoparticles coated with chitosan for use as a heating agent and MRI contrast agent in biomedical applications

Nanoferrites, day by day become the center of attraction due to their acceptability as contrast agents due to their enhanced properties. Wet chemical coprecipitation was used to prepare Mn1-xZnxFe2O4 nanoparticles. In order to apply the material for biomedical applications, the nanoferrites were also coated with the biodegradable material chitosan. XRD spectra confirmed the spinel ferrite configuration. It also showed that the structure was face centered cubic. TEM and HRTEM images in both bright- and dark- fields were used to analyze the surface structure and particle size. The particle size was observed below 10 nm. From EDS analysis, the elemental composition of the as-dried and coated materials was determined. No impurity was observed in the material. Along with XRD, FTIR also confirmed the formation of bare and coated spinel ferrites. Two characteristic bands were observed for the material that is also the basic features of the ferrite material. Using an M−H diagram, the variation in saturation magnetization and coercivity as a function of zinc content in the coating was investigated in great depth. It was observed that the saturation magnetization vary a little for coating material. The polydispersity index (PDI) and hydrodynamic diameter of the chitosan-coated solution were determined at 2 mg/ml and 4 mg/ml concentrations. It was seen that Mn0.8Zn0.2Fe2O4 and Mn0.6Zn0.4Fe2O4 at both concentrations were exhibit PDI value within the permissible range. It was discovered through an in-vitro cytotoxicity test on HeLa cancer cells that all of the coated samples were nontoxic to use. Relaxivity values were calculated using MRI images. The relaxivities progressively decreased in value as the zinc ions rose. TOF tests were used to examine the effect of the contrast agent. The samples’ heating profiles were examined to determine whether coated nanoferrites were suitable for use in applications involving hyperthermia. It has been noted that the Mn0.6Zn0.4Fe2O4 sample is appropriate for biomedical applications involving hyperthermia.

GdFe-based nanostructured thin films with large perpendicular magnetic anisotropy for spintronic applications

In this study, we investigated the impact of geometric factors on the magnetic anisotropy of Gd-Fe alloy thin films deposited on nanoporous alumina membranes. By synthesizing Gd-Fe alloy nanostructure thin films with different hole diameters (ranging from 45 to 90 nm) and keeping the layer thickness and lattice parameters fixed at 45 nm and 105 nm, respectively, we observed a significant perpendicular magnetic anisotropy (PMA) in samples with hole diameter above 65 nm. The transition from in-plane to out-of-plane magnetization in Gd-Fe alloy nanostructure thin films occurred at a critical antidot hole diameter of 75 nm. The observed variations in coercivity and remanence with the nanohole diameter are attributed to substantial changes in the magnetization mechanisms induced by the nanoholes. This novel induction of PMA in Gd-Fe alloy nanostructure thin films through the manipulation of geometric parameters in the antidot arrays opens new possibilities for tailoring the magnetic behavior of ferromagnetic metals with pronounced PMA.

Micromagnetic simulation of Nd-Fe-B demagnetization behavior in complex environments

With the continuous expansion of the application range of Nd-Fe-B permanent magnetic materials, it becomes increasingly necessary to understand their magnetic performance under different working conditions. Currently, there is limited research on the magnetization characteristics of Nd-Fe-B in complex environments. In this study, a theoretical model considering demagnetizing field, thermal effects, and force-magnetic coupling was established to investigate the demagnetization behavior of Nd-Fe-B under the combined influence of temperature, pressure, and magnetic field. To address the high cost and implementation difficulties associated with demagnetization experiments in complex environments, as well as the limitations of general hysteresis models in terms of research scale, a micromagnetic numerical simulation method incorporating the theoretical model was adopted. The simulation was performed using COMSOL Multiphysics, which allows for multi-physics field coupling. The demagnetization behavior of Nd-Fe-B in complex environments was calculated. The demagnetization curves of Nd-Fe-B under different combinations of temperature, pressure, and magnetic field were obtained. From the perspective of magnetic moment motion, the demagnetization mechanism of Nd-Fe-B was analyzed. Furthermore, the variations in coercivity, Curie temperature, and critical demagnetizing pressure of Nd-Fe-B in complex environments were summarized. These findings provide theoretical guidance for the application of Nd-Fe-B permanent magnetic materials in complex working environments.

Spatially Tuned Properties in a Bulk Fe–Co Soft Magnetic Alloy via Transverse Induction Annealing and Feasibility Study for Motor Applications

Electric vehicle adoption has seen a dramatic upward trend in the last decade. Maximal efficiency of electric motor technology for maximum range, achieved by minimizing losses experienced by motor stator and rotor, is limited by a trade‐off with high strength, as necessary to withstand torque experienced during operation. Spatial tailoring of magnetic and mechanical properties for optimized magnetic performance while retaining sufficient mechanical strength is a desirable pathway toward improved performance. Here, radiofrequency transverse induction annealing is demonstrated as a novel pathway to continuous spatial variation in microstructure of bulk crystalline soft magnetic alloys, providing a novel processing route to spatially tuned properties. Via local control of grain size, magnetic and mechanical properties may be separately prioritized as functions of position, enabling optimized stator laminations with reduced losses while retaining requisite mechanical strength. Experiment and finite element modeling demonstrate that a cylindrical induction coil can impose significant microstructure and property variation in a Fe–Co bulk crystalline soft magnetic alloy. A basic feasibility study follows, examining improved performance of a motor containing a stator with radial variation in coercivity. Results indicate future potential for co‐optimization of spatial thermal processing of magnetic laminations with motor designs for unprecedented performance.

Quantized resistance revealed at the criticality of the quantum anomalous Hall phase transitions

In multilayered magnetic topological insulator structures, magnetization reversal processes can drive topological phase transitions between quantum anomalous Hall, axion insulator, and normal insulator states. Here we report an examination of the critical behavior of two such transitions: the quantum anomalous Hall to normal insulator (QAH-NI), and quantum anomalous Hall to axion insulator (QAH-AXI) transitions. By introducing a new analysis protocol wherein temperature dependent variations in the magnetic coercivity are accounted for, the critical behavior of the QAH-NI and QAH-AXI transitions are evaluated over a wide range of temperature and magnetic field. Despite the uniqueness of these different transitions, quantized longitudinal resistance and Hall conductance are observed at criticality in both cases. Furthermore, critical exponents were extracted for QAH-AXI transitions occurring at magnetization reversals of two different magnetic layers. The observation of consistent critical exponents and resistances in each case, independent of the magnetic layer details, demonstrates critical behaviors in quantum anomalous Hall transitions to be of electronic rather than magnetic origin. Our finding offers a new avenue for studies of phase transition and criticality in QAH insulators.

Tunable magnetic properties of CoPt nanoparticles: Impacts of phase coexistence and thermal annealing

Nanostructured materials such as CoPt nanoparticles with tunable hard magnetic properties are desirable for a wide range of technological applications. In CoPt nanoparticle systems, a structurally disordered fcc phase may be transformed into an ordered fct L10 phase via annealing. However, the effects of this thermally induced disorder to order transition on the magnetic properties and phase coexistence still need to be understood. Here, we have studied these effects in Co50Pt50 nanoparticles, which were prepared by chemical reduction combined with ultrasound. By varying the annealing temperatures from 450 °C to 700 °C for 1 h, we observe that the magnetic properties are heavily dependent on the annealing temperature. The nanoparticles annealed at 500 °C exhibit the highest coercivity, while the 600 °C annealed nanoparticles possess the largest saturation magnetization. We demonstrate the variation in coercivity with annealing temperature follows that of the order parameter. This study establishes, for the first time, a correlation between the order parameter and the coercivity for annealed CoPt nanoparticles and paves a pathway for the development of nanostructured magnets with tunable magnetic properties.

Temperature evolution of pseudo magnetic properties and vortex state in Fe71Ga29 thin films

We report on the temperature evolution of pseudo magnetic properties and vortex state in Fe71Ga29 thin films at different substrate temperatures (RT-25 °C, 50 °C, 75 °C, and 150 °C) using minor loop analysis and first-order reversal curves respectively. Phase purity of Fe71Ga29 thin films confirmed with grazing incidence X–ray diffraction, which confirms the A2-type disordered phase. The minor loop parameters such as energy loss coefficient WF0 (362 kOe.emu/cc to 278 kOe.emu/cc) and trough depth coefficient WR0 (67.30 kOe.emu/cc to 50.23 kOe.emu/cc) values drop as grain size increases due to a reduction in defects as a result of an increase in substrate temperature. First-order reversal curves allow us to estimate the coercivity variation and switching field distribution that allow us to get information about magnetic interactions between the domains. Additionally, the contour plots of FORC and MFM phase images infer the coexistence of multidomain and Vortex State (VS) in all the Fe71Ga29 thin films deposited at different substrate temperatures.

Development of Lead Free Magnetoelectric Materials for Magnetic Field Sensor applications

(100-x) Na0.5Bi0.5TiO3 (NBT)-(x) NiFe2O4 (NFO)(x = 0, 20, 40, 60, 80 and 100) composites are synthesized using conventional solid state reaction method. Crystal structure studies are performed by using X-ray Diffraction technique (XRD) and the Rietveld analysis of XRD patterns confirms the co-existence of cubic (NFO) and rhombohedral (NBT) symmetry with Fd- 3m and R3c space groups, respectively. Micro-structural study reveals the formation of combination of composite phases and its inter-coupling grains. The average grain sizes and area percentage of each phase for the composites are calculated using Image J software. The Magnetisation versus Magnetic field (M-H) hysteresis loops show soft magnetic behavior of composites with variation in Saturation magnetization (MS) and Coercivity (HC). A maximum MS (34 emu/g) and low HC (15 Oe) is obtained for (80) NFO - (20) NBT composite.The Polarization – Electric field (P-E) analysis shows that the maximum saturation polarization (PS) is obtained for (60)NBT-(40)NFO sample and is attributed to the leakage current generated by conductive NFO phase. The coupling between the ferrite and ferroelectric phase is studied based on the magnetoelectric voltage coefficient(αME). The maximum (αME) of 1.82 mV/cm-Oe is obtained for (80)NBT -(20)NFO sample and this is almost 80% higher than the previously published literature on NBT-NFO composites. This can be attributed to the uniform distribution of grains with each ferroelectric phase surrounded by ferrite phase as shown in the morphological study.

Tailoring anomalous Hall effect by spin–orbit coupling in epitaxial Au/Fe4N bilayers

Anomalous Hall effect (AHE) is one of the most fascinating topics in condensed matter physics related to spin–orbit coupling (SOC). In this paper, we report on the AHE of high-quality epitaxial Au/Fe4N bilayer films, which were grown by a plasma-assisted molecular beam epitaxy system. A scaling involving multiple competing scattering mechanisms and a shunting model were adopted to analyze the AHE in detail. Compared with Fe4N single layers and Cu/Fe4N bilayers, the AHE of Au/Fe4N bilayers is dramatically modified by strong SOC of the Au layer. Analysis has shown that aside from extra scatterings from Au atoms that diffused from an Au layer to a Fe4N layer, both spin Hall effect of Au and magnetic proximity effect near the Au/Fe4N interface contribute to the modification of the AHE. Variation of coercivity with the change of current, which could be attributed to spin–orbit torque, implies that the measured AHE is a combination of the AHE of Fe4N and strong SOC of Au.

Effect of Ni2+ substitution on structural, magnetic and electrical traits of Ba1-xNixFe2O4

Nickel substituted Barium ferrites is synthesized by citrate gel method. Nickel which is transition metal used to tailor the properties of the Ba spinel ferrites. The characterization techniques such as thermogravimetry–differential thermal analysis (TG-DTA), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FTIR), ultra-violet diffuse-reflectance spectroscopy (UV-DRS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), Raman analysis and direct current (DC) electrical conductivity are used to investigate various properties. XRD and rietveld refinement confirmed the existence of orthorhombic as well as cubic phase with the decrease in lattice parameters in orthorhombic phase. FTIR spectra confirmed the presence of absorption bands for tetrahedral and octahedral sites. Tauc’s plots accredited the increase in band gap with increase in Ni content. The magnetic hysterisis loop exhibited large variation in coercivity and remanence. Increased Yafet-Kittel (Y-K) angle indicated redistribution of ions amongst the sites strenthening the A-B exchange interactions. DC electrical conductivity observed the conductive switching from n-type to p-type. Thermally activated charge carriers and hopping of electrons boost drift mobility. The activation energy of conduction is observed in the range of 0.40 to 0.85 eV. Raman peaks confirmed formation of orthorhombic as well as cubic phase.

Synthesis and characterization of thermally treated Co1-xFe2+xO4 (x = 0.0 –0.8) spinel nano ferrite

We report the effect of surplus-Fe-content, and thermal annealing on the properties of sol gel auto-combustion synthesized Co1–xFe2+xO4 (x = 0.0–0.8) spinel ferrites. X-ray diffraction (XRD), magnetic measurements, Fourier transform infrared (FTIR) spectroscopy, Ultraviolet–visible (UV–Vis) are used to monitor the effect of excess Fe-content, and thermal annealing dependence of properties, and correlation among them. XRD validates presence of spinel nanoferrite (31.54 – 44.89 nm) phase, minor presence of α-Fe2O3 phase was also detected. Results reveal that variation of Fe-content leads to: i) variation of lattice-parameter, re-distribution of Fe3+. Co2+ ions on A, B-site, ii) alteration of inversion degree, disorder, iii) modification of saturation magnetization due to spin disorder at surface, iv) variation of coercivity, and related grain size imply that studied ferrites are in single-multi domain overlap regions, while squareness-ratio indicates variation of inter-grain interaction, isotropic behaviour of multi-domain particles; iv) fine-tuning of bandgap (1.35 – 1.5 eV) via changes in cationic-distribution and lattice-parameter, v) variation of Debye temperature, suggests modification of lattice vibrations. Current work implies strong correlation between bandgap magnetic, structural properties.

Magnetic Properties Regulation of FeGa and FeGaNi Films with Oblique Magnetron Sputtering

Magnetic FeGa and FeGaNi films with an in-plane anisotropy were deposited by employing oblique magnetron sputtering. With the increase in oblique angle, the crystallite size of FeGa decreases, which indicates that oblique sputtering can refine the crystallite size. The remanence ratio of FeGa films increases from 0.5 to 0.92 for an easy axis, and the coercivity increases with the decrease in the crystallite size. The calculated static anisotropic field shows that the in-plane magnetic anisotropy can be induced by oblique sputtering and the strength increases with the oblique sputtering angle. After doping Ni by co-sputtering, FeGaNi films exhibit a stable remanence ratio at 0.8, low coercivity and good anisotropy. With the low sputtering power of the Ni target, there is a competitive relationship between the effect of crystallite size and Ni doping which causes the coercivity of FeGaNi films to first increase and then decrease with the increase in the oblique angle. The FeGaNi film also shows high anisotropy in a small oblique angle. The variation of coercivity and anisotropy of FeGaNi films can be explained by the crystalline size effect and increase in Ni content. For the increasing intensity of collisions between FeGa and Ni atoms in the co-sputtering, the in-plane magnetic anisotropy increases first and then decreases. As a result, the magnetic properties of FeGa films were examined to tailor their magnetic softness and magnetic anisotropy by controlling the oblique sputtering angle and Ni doping.

Positron annihilation and magnetic studies of gamma irradiated nickel ferrite nanoparticles sintered at various temperature

The effects of gamma irradiation on structure and magnetic properties of nickel ferrite nanoparticles, prepared by the sol-gel method and sintered at 300, 500 and 900 °C, are studied through X-ray diffraction, positron annihilation lifetime spectroscopy, coincidence Doppler broadening spectroscopy and vibrating sample magnetometer. The prepared samples were irradiated with gamma rays from 60Co, 137Cs and 22Na for 1, 2 and 3 weeks that received 0.47, 0.94 and 1.41 rad dose of radiation. The XRD patterns showed that the prepared and irradiated samples are single phase with cubic spinel structure. The cation distribution, lattice constant, average crystallite size and lattice strain were obtained by the Rietveld refinement of XRD patterns and their variations with irradiation depend on sintering temperature and therefore the particle size. Scanning electron microscopy confirmed formation of nanoparticles. Positron annihilation lifetime and coincidence Doppler broadening measurements showed that for prepared samples with an increase in sintering temperature the size of vacancies increase while their concentrations decrease. It is observed that the effect of gamma radiation on samples depend on sintering temperature or particles size of samples. Also, the type of defects in sample sintered at 300 °C recognized different from samples sintered at 500 and 900 °C. Saturation magnetization and coercivity increased for prepared samples with increase in sintering temperature. The variations of saturation magnetization and coercivity with gamma irradiation for samples sintered at various temperature were different and explained with variation in cation distribution and surrounding environment of vacancies in samples. The measurements showed that samples with more vacancy concentration undergo more cation redistribution due to gamma radiation.

Effect of rare earth (Nd3+) metal doping on structural, morphological, optical and magnetic traits of Zn–Mg nano-ferrites

Herein, we report the synthesis of Zn0.7Mg0.3NdxFe2–xO4 (where, x = 0.0, 0.01, 0.02) ferrite nanoparticles by employing the sol–gel auto-combustion technique. The X-ray diffraction (XRD) pattern suggests the formation of a pure cubic structure, without any impurity phase, with an Fd3m space group at room temperature. With increasing doping amount, the crystallite size is reported as 35–41 nm, while the lattice parameters rise from 0.8381 to 0.8395 nm. Field emission scanning electron microscopy (FESEM) images show the formation of spherical grains with agglomerated morphology in all the samples, with grain sizes ranging from 49 to 103 nm. Energy dispersive X-ray spectroscopy (EDX) and elemental mapping investigation confirm the chemical purity of all the samples. Fourier transform infrared (FTIR) analysis shows the presence of two prominent peaks around 440 and 560 cm−1 that correspond to the octahedral and tetrahedral positions. In addition, the existence of five Raman active vibrational modes in all produced specimens again confirms the structural purity of all the samples. The M−H curve shows that saturation magnetization (Ms) first increases from 14.98 to 28.22 emu/g and then decreases to 18.98 emu/g with increasing doping amount. This is due to the A-B type super-exchange interaction for the synthesized samples. The variation in coercivity (Hc) and magnetic anisotropy (K1) suggest the thermal stability of all the samples and can be utilized in transformers and solenoids.

Magnetic characterisation of London's airborne nanoparticulate matter

Iron-bearing particulate matter produced by vehicle emissions is known to be toxic. To better quantify potential health risks, we have conducted the first magnetic study of a time-series of London's inhalable particulate matter (<10 μm, PM10), captured by three monitoring stations in central London (Marylebone Road, Earl's Court Road and Oxford Street) through 2010 and 2012. We conducted room-temperature analysis on all the samples, and a limited number of samples were analysed at both high and low temperatures. The high-temperature measurements identified magnetite as the dominant magnetic phase. The low-temperature measurements revealed high numbers of nanoparticles, which, assuming magnetite, are in the grain-size range 1–4 nm. It is estimated that as much as ∼40% of the total magnetic signal at 10 K is from particles <4 nm, that are magnetically ‘invisible’ at room-temperature and are being routinely under-estimated in room temperature-based magnetic studies. From the low-temperature measurements, the total concentration of magnetite was estimated at ∼7.5%, significantly higher than previously reported. The room-temperature magnetic data were compared with other pollution data, e.g., NOX and PM10, and meteorological data. Mass-dependent terms like the saturation magnetisation were found to display a strong correlation with NOX and PM10, indicating a common source for these pollutants, i.e., vehicle emissions. Magnetic coercivity measurements, which are independent of abundance, and provide information on grain-size, were consistent across all three sampling localities, again suggesting a major dominant source. Relatively small variations in coercivity were correlated with meteorological events, e.g., temperature and precipitation, suggesting preferential removal of larger airborne grains, i.e., >50 nm.

Enhanced structural, electromagnetic and absorption features of CoSm ferrite-metamaterial absorbers through synergistic effects

Currently, materials with outstanding absorption abilities, such as thin size, better absorbing power, and light weight are the need of industry to resolve the electromagnetic issues. However, the research on optimizing the composition of the material, microstructure and the structure of the absorber are also the important factors for enhancing the absorption features. A metamaterial microwave absorber (MMA) based on nano ferrites with desirable absorption peaks is proposed and simulated. Sol-gel auto combustion route is used to prepare the nanosized Sm doped Co ferrite with Co1+xSmxFe2-2xO4 at x = 0.00, 0.03, 0.06, 0.09, respectively. XRD, VSM, FESEM, and VNA were employed to evaluate the structural, magnetic, morphological, and dielectric features. Rietveld refinement of the XRD patterns of samples was evaluated. Refined parameters show the spinel phase's emergence and the Fe2O3 phase. Grain size and crystallite size were increased with Sm doping in Co ferrite. Electromagnetic studies depicted that the highest dielectric constant value was found at x = 0.09 and the minimum value at x = 0.03, respectively. Sm doped Co ferrite at x = 0.09 depicted high Q values at higher frequencies. The coercivity values first decreased and then increased. All samples exhibit variations in coercivity and magneto-crystalline anisotropy constant. This variation was attributed to the super-exchange interactions and strong LS coupling of the cations. The multiple absorption peaks are attained for TE-polarization, and the absorptivity is considerably improved for x = 0.09. The proposed absorber simulated from CST depicted the absorption peaks of the S-band and C-band of the microwave regime. The synergistic effects among the metamaterial and ferrite layers may enhance the absorption feature and would be useful for satellite communication applications.