Remanent Coercivity Research Articles

Investigation of Structural, Elastic and Magnetic Properties of CoCr2-xZrxO4 Nanoparticles.

This study investigates the impact of zirconium substitution on the structural, elastic and magnetic properties of CoCr2O4 nanoparticles. A series of CoCr2-xZrxO4 nanoparticles, x = 0.00, 0.05, 0.10, 0.15 and 0.20, are synthesized via the co-precipitation method. X-ray diffraction (XRD) patterns affirm the formation of single-phase cubic structure with the space group Fd3m. Special attention is given to accurately calculating the average crystallite size (D) and lattice parameter (a) using Williamson-Hall (W-H) analysis and the Nelson-Riley (N-R) extrapolation function, respectively. The increase in Zr4+ content leads to a reduction in crystallite size and an increase in the lattice parameter. Elastic properties are estimated from force constants and the lattice constant, determined from FTIR and XRD, respectively. The observed changes in the elastic constants are attributed to the strength of interatomic bonding. The stiffness constants decrease, while Poisson's ratio increases with increasing Zr4+ content, reflecting the increase in the ductility of the prepared samples. As the Zr4+ content increases, the stiffness constants decrease, and Poisson's ratio increases, reflecting enhanced ductility of the samples. Furthermore, as Zr4+ content rises, Young's modulus, the rigidity modulus and Debye temperature decrease. The magnetic hysteresis loop measurements are carried out at room temperature using a vibrating sample magnetometer (VSM) over a field range of 25 kg. Unsubstituted CoCr2O4 exhibits ferrimagnetic behavior. As Zr4+ content increases, saturation magnetization (Ms) and magnetic moment decrease, while remanent magnetization (Mr) and coercivity (Hc) initially decrease up to x = 0.10, then increase with further increases in x. The novel key of this study is how Zr4+ substitution in CoCr2O4 nanoparticles can effectively modify their elastic moduli and magnetic properties, making them suitable for various applications such as flexible electronics, protective coatings, energy storage components and biomedical implants.

Structure and tunable temperature coefficient of magnetization of Mn4-xGaxC alloys prepared by induction melting method

Abstract The magnetization of most magnetic materials decreases monotonically with increasing temperature. In this work, we found that the temperature coefficient of magnetization of Mn4-x Ga x C alloys can be tuned from negative values to positive values by controlling the composition x. The antiperovskite-type Mn4-x Ga x C (0.05≤x≤0.75) alloys were prepared by using induction melting method, which is more efficient in large-scale production and obtaining full-density alloys in comparison with the traditional solid-state-reaction method. The values of the temperature coefficient of magnetization of Mn4-x Ga x C change continuously from negative to positive with decreasing x. The Mn4-x Ga x C alloys with highly thermal-stable magnetization is expected to present in the composition range of 0.15<x<0.25. The saturation magnetization of Mn4-x Ga x C increases with increasing x, owing to the reduced number of antiferromagnetically coupled Mn atoms at the cubic corner with the face-centered Mn atoms. Most Mn4-x Ga x C alloys with varying x display near-zero remanent magnetization and coercivity at room temperature. The Currie temperature of Mn4-x Ga x C decreases with increasing x. The x-ray photoelectron spectra of Mn 2p, Ga 2p, and C 1 s reveal distinct splitting due to the diverse chemical states of these atoms at different lattice positions and/or phases. Our work has developed a class of alloys capable of offering a desired temperature coefficient of magnetization across a broad temperature range, thereby offering a method to manipulate the thermodynamics of magnetization.

Impact of substituting Cu2+/Ce3+ cations on the structural, magnetic and electrical properties of cobalt nano ferrites

The nano ferrite compounds Co1-xCuxFe2-yCeyO4 (with x values of 0.0, 0.25, 0.5, and 0.75, and y values of 0.0, 0.03, 0.06, and 0.09) were synthesized through the sol-gel auto-combustion method. The characteristics of spinel ferrites were tailored by creating nano ferrites with desirable properties, which were then sintered at 1150 °C for 2 h in the presence of rare earth (Ce3+) and transition metals (Cu2+). They were investigated using dielectric, FTIR, FESEM, XRD, VSM, and DC electrical resistivity experiments. XRD examination verified the samples' cubic spinel structure by measuring the average crystallite size, x-ray density, and lattice constant. FESEM images revealed grain sizes ranging from 41.07 to 156 nm. FTIR spectra in the range of 415 cm−1 to 430 cm−1 further supported the substitution of Cu2+/Ce3+ ions in the tetrahedral sites, indicated by an increase in the lattice parameter. Measurements of the remanence ratio, saturation magnetization, anisotropy constant, coercivity, and magnetic moment, among other magnetic characteristics, were made. Higher concentrations of Cu2+/Ce3+ ions were found to considerably reduce magnetic saturation (Ms), coercivity (Hc), and remanence (Mr). These materials were semiconducting because their activation energy varied between 0.52 and 0.62 eV, and their DC resistivity increased with increasing Cu2+/Ce3+ concentration. Above 1 MHz, the dielectric properties became frequency-independent and decreased with increasing frequency. These ferrites seem highly potential for devices working at high frequency.

Construction of Tb-rich shells via novel interdiffusion approach to tackle coercivity-remanence trade-off

The strategic introduction and efficient utilization of heavy rare earth elements within Nd-Fe-B-based permanent magnets are instrumental in achieving an optimal balance between remanence (Br) and high coercivity (Hcj). Herein, we propose a novel interdiffusion approach based on hydrogen decrepitation (HD) for the cost-effective and high-performance sintered Nd-Fe-B magnets. With the aim of generating continuous Tb-rich shells on the grain surface, which favors high Br and high Hcj, strip cast (SC) flakes homogeneously mixed with 0.9 wt% Tb were processed by the HD. It is shown that the formation of (Nd, Tb)-Fe-B by the interdiffusion of Nd-Fe-B and Tb during de-hydrogenation, as well as the interdiffusion of Nd-Fe-B and (Nd, Tb)-Fe-B during sintering and tempering, is the key to the construction of Tb-rich shells. As a result, a magnet (Mag-Tb&HD) with maximum magnetic energy product ((BH)max) of 52.21 MGOe was achieved, which is superior to magnet prepared form SC flakes containing 0.9 wt% Tb (Mag-Tb&SC, (BH)max=49.36 MGOe) and the magnet prepared by adding 0.9 wt% Tb to the jet milling (Mag-Tb&JM, (BH)max=50.41 MGOe).

Size-strain distribution analysis from XRD peak profile of (Mg, Fe) co-doped SnO2 nanoparticles fabricated using chemical co-precipitation route

In this study, we synthesize pristine and (Mg, Fe) co-doped SnO2 nanoparticles using the chemical co-precipitation method, where the Mg doping amount is fixed (2 mol%) and the amount of Fe is varied between 2 and 6 mol%. The narrow and sharp natures of intense XRD peaks notify that the crystallinity is pretty well. The formation of the single-phase tetragonal rutile type structure of all prepared compounds has been identified by Rietveld refinement, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. Moreover, the well incorporation of Fe and Mg in SnO2 and absence of any other unexpected elements are confirmed by the energy dispersive X-ray spectroscopy. How the co-doping of Mg and Fe alter the crystallite size, microstrain, and dislocation density of the prepared samples have been investigated by Scherrer method with various modified version of it, Williamson-Hall method (W–H) in three factions (UDM, USDM, and UDEDM), Size strain plot (SSP) method, Halder-Wagner (H–W) method, Wagner-Aqua (W-A) method, and Warren-Averbach (WA) method. The obtained crystallite size using the WA method is smaller than the other methods and Scherrer-based methods show much comparable (except SLMSE) sizes. Additionally, the W–H, H–W, SSP, and W-A plots show almost similar tendency of decreasing crystal size, increasing dislocation density and lattice strain with increasing doping. The scanning electron microscopy (SEM) profiles revealed that the synthesized nanoparticles are agglomerated in nature, where the agglomeration increases with decreasing crystal size. The magnetic response of the prepared samples revealed a weak ferromagnetic (or soft magnetic) nature, where saturation magnetization increased due to doping, and a reducing trend of remanent magnetization and coercivity was explored which indicates the phase transition from ferromagnetic to paramagnetic. However, this soft magnetic nature was modified with the influence of defects like changes in lattice parameters, strain, and oxygen vacancy. This phase transition at higher doping concentration makes our nanomaterial as a suitable contender for memory devices, hyperthermia treatment, and photothermal effect.

Shape-controlled electro-synthesis of pyrrhotite

Recently, iron sulfide nanomaterials have drawn increased interest, due to their novel properties and extensive applications depending on their structure. To date, various methods have been employed for the synthesis of iron sulfide nanostructures with different shapes and morphologies. The synthesis method of iron sulfide nanomaterial is a challenge, as a small variation in sulfur content can lead to formation of different phases of iron sulfide. In this study, iron sulfide nanostructures were synthesized using our fast, simple, efficient, economical and environmentally friendly method in an electrochemical cell containing two iron sheets as electrodes in an aqueous solution of sodium sulfide. This method, with many advantages such as low-toxicity, low cost and easy handling, helps to control the properties of the products through the synthesis by tuning the growth conditions. Here, the influence of applied voltage ranging from 5 V to 25 V and annealing temperatures of 200 °C and 800 °C on the structure and magnetic properties of the products were studied. The samples were analyzed by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). XRD patterns confirmed the formation of monoclinic and hexagonal pyrrhotite at 200 °C and 800 °C, respectively. Based on SEM images, pyrrhotite in different shapes, such as quasi-spherical, feathers, sheets and flower-like structures, are formed depending on the applied voltage and annealing temperature. According to VSM results, all samples annealed at 200 °C are magnetically soft with only a little hysteresis, but the magnetization increases from 2.3 emu/g to 10.1 emu/g when applied voltage varies from 5 V to 25 V. All samples annealed at 800 °C exhibit an antiferromagnetic behavior. With increasing the applied voltage, the value of remanence magnetization and coercivity increases up to ∼2000 Oe and ∼0.14 emu/g, respectively.

Assessing lunar paleointensity variability during the 3.9 - 3.5 Ga high field epoch

Numerous paleomagnetic studies suggest that a lunar dynamo, with surface field intensities potentially as high as 40-100 µT, existed between ∼3.9 Ga and ∼3.5 Ga. This period is referred to as the High Field Epoch (HFE). However, the debate over the origin of magnetization recorded in lunar rocks still persists. In addition, whether the Moon could have sustained a continuously strong dynamo during the HFE remains unclear. To unravel the origin of magnetization preserved in lunar rocks and to better characterize the evolution of the ancient lunar dynamo, we conducted a comprehensive set of experiments including rock magnetic tests, electron microscopy, and paleomagnetic investigations on four HFE-aged Apollo 11 mare basalt samples: 10003, 10044, 10069, and 10071. Rock magnetic experiments and electron microscopy indicate that the remanence carriers are kamacite grains of varying sizes and domain states. Sample 10003 recorded a paleointensity of 54.10 ± 4.66 µT. Sample 10044, which was shocked (peak pressure >5 GPa), did not preserve a stable high coercivity remanent magnetization. Samples 10069 and 10071 recorded paleointensities of 61.46 ± 26.09 µT and 10.69 ± 2.87 µT, respectively. A series of hydrostatic pressure experiments, isothermal remanent magnetization (IRM) acquisition experiments, and viscous remanent magnetization (VRM) tests preclude the possibility of our samples containing shock remanent magnetization from transient impact-generated fields, IRM acquisition from exposure to spacecraft fields, and VRM acquisition from exposure to the Earth magnetic field. Overall, our study suggests that the source of these magnetizations was likely the lunar dynamo and may indicate nearly order-of-magnitude magnetic field fluctuations during the HFE.

Influence of preparation method on structural, optical and magnetic properties of synthesized Zn0.5Mg0.5−xNixFe2O4 nano-ferrite

Structural, optical, and magnetic properties of ferrite series with chemical formula Zn0.5NixMg0.5−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3 and 0.4) were investigated. Co-precipitation and sol–gel methods were used to synthesis the samples and to investigate further the influence of these preparation methods on the properties of Zn0.5NixMg0.5−xFe2O4 nano-ferrites. X-ray diffraction and Fourier-transform infrared spectroscopy revealed that the samples crystallize in a cubic spinel structure with space group Fd3m:1. The crystallite size of Zn0.5NixMg0.5−xFe2O4 nanoparticles was decreased from 19.15 to 11.65 nm with increasing Ni content for the samples of co-precipitation method, while the opposite behavior was observed in case of sol–gel method which was increased from 13.90 to 21.90 nm. Moreover, the optical investigation by UV-visible spectroscopy revealed that the energy band gap of the samples of co-precipitation method ranged (6.04–6.08) eV compared to (4.44–4.50) eV of sol–gel method. For both methods, substitution of Ni+2 by Mg+2 in Zn0.5NixMg0.5−xFe2O4 affects the remanent magnetization (Mr), coercivity (Hc) and saturation magnetization (Ms) suggesting the super-paramagnetic behavior of the samples. The substitution of Ni resulted in small values of coercivity ranged 0.758 to 164.62 Oe. The Ms was ranged 20.39 to 127.57 emu g−1 and an enhancement in magnetization was observed which increases the value of Ms that was found to be maximum with x = 0.4 of co-precipitation method (127.57 emu g−1). The magnetic behavior of synthesized Ni doped nanoparticles makes them suitable candidate for sensing and high-frequency applications and for use in hyperthermia treatment. The characterization outcomes may recommend that co-precipitation method is preferred over sol–gel method for refined structure and preferable properties of Zn0.5NixMg0.5−xFe2O4 nanoparticles.

Tinospora cordifolia-assisted synthesis of silver ferrite nanoparticles: a multifunctional approach to photocatalytic degradation of reactive blue-13 dye, anti-bacterial efficacy, and antioxidant properties

Tinospora cordifolia-assisted synthesis of silver ferrite nanoparticles: a multifunctional approach to photocatalytic degradation of reactive blue-13 dye, anti-bacterial efficacy, and antioxidant properties

Magnetic, Optical, Electrical and Antimicrobial Properties of MnCuZnFe2O4 Nanoparticles

AbstractThe Mn0.92Cu0.08‐yZnyFe2O4 (y=0.02, 0.04, 0.06 and 0.08) nanoparticles (MCZF NPs) were synthesized via the hydrothermal process at low operating temperature. The MCZF system generated a cubic spinel structure as seen by the X‐ray diffraction patterns. The average crystallite size was observed to be increasing from 25 to 30 nm. The broad (γ1) and narrow (γ2) absorption bands were seen in FTIR spectra and the cation distributions at tetrahedral (A) and octahedral (B) sites, respectively, was indicated. The surface morphology was analyzed using electron microscopy. Clarification was provided for the dependence of the optical bandgap shift (Eg~1.96–2.15 eV) on the concentration of substituent. The superparamagnetic nature of MCZF can be advantageous for biomedical applications and it was demonstrated by the magnetization versus applied magnetic field (M−H) loops. Small values of remanence magnetization (Mr) and coercivity (Hc) were found using magnetization versus magnetic field (M−H) curves at y=0.02, 0.04, 0.06, and 0.08. This proved that MCZF NPs exhibited the superparamagnetic behavior. The cation distribution at two sublattices was also estimated using a two‐sublattice model. The greatest zone of inhibition in an antibacterial study of MCZF (produced by the green method) was 10.8 mm for Pseudomonosa aeruginosa and 9.4 mm for Staphylococcus aureus.

Magnetoviscous properties of Fe-based amorphous magnetic fluids

Fe-Zr-B amorphous magnetic fluid has been prepared by a chemical reduction method. X-ray diffraction, transmission electron microscope and vibrating sample magnetometer have been utilized for the characterization of the structure, morphology, and magnetic property of Fe-based amorphous magnetic fluids. Besides, the magnetoviscous properties were also investigated. The results indicate that the Fe-Zr-B particles possess a non-crystalline structure with a particle size below 30 nm. The saturation magnetization of the amorphous particles is approximately 55 emu/g, exhibiting extremely low remanent magnetization and coercivity. We also investigated a parameter named Δη*=ηup-ηdown/ηdown, which characterizes the hysteresis effect between viscosity vs magnetic field. The results show that the relatively reduced viscosity △η* is negative below 124 mT, and becomes positive when the magnetic field is higher than 124 mT. We reveal the inverse associations between viscosity and magnetic fields, which can be attributed to the combined influence of thixotropy and magnetic fields. These discoveries present a fresh perspective on the magnetoviscous behavior of magnetic fluids.

Adjusting the gas detection characteristics of NiFe2O4 spinel ferrite nanoparticles through the introduction of Zn doping

Nickel ferrite nanoparticles doped with zinc were synthesized at a lower reaction temperature of 180 °C. The research delved into their structural, optical, dielectric, and magnetic properties. These nanoparticles exhibited a distinct cubic spinel structure, with crystallite sizes ranging from 33 to 51 nm. FTIR analysis revealed metal oxide stretching vibrations between 400–600 nm. FESEM and HR-TEM examinations unveiled irregularly shaped nano-particles. XPS analysis disclosed the chemical states of Zn2+, Fe3+, and Ni2+ ions. Mossbauer spectra exhibited two sextet patterns related to tetrahedral (A) and octahedral (B) sites, plus a weak doublet pattern. Magnetic tests showed a decrease in saturation magnetization (Ms) but an increase in remanent magnetization (Mr) and coercivity (Hc) values upon doping.

Monitoring the Centennial Variation of Heavy Metals in Lake Sediments and Influencing Factors Using Environmental Magnetism and Machine Learning Methods

The association between the magnetic properties of lake sediments and heavy metal(loid)s (HMs) is well-documented; however, their correlation with the chemical fractions of HMs remains under-investigated. Developing a robust workflow for predicting HMs risk utilizing various machine learning techniques in conjunction with magnetic analysis presents a complex challenge. This study assessed the predictive efficacy of nine machine learning models for determining the chemical fractions of HMs, employing magnetic parameters derived from sediment cores in a large, shallow lake. These models encompassed random forest, support vector machine, relevance vector machine, extreme gradient boosting, principal component regression, multivariate adaptive regression splines, gradient boosting with component-wise linear models, and lasso and elastic-net regularized generalized linear models. The support vector machine model demonstrated superior performance, achieving coefficient of determination values surpassing 0.8 in both training and testing phases. Through interpretable machine learning approaches, key drivers of HMs were identified among magnetic and physicochemical indicators. Magnetic susceptibility values, high coercivity remanent magnetization, ratios of anhysteretic remanent magnetization to magnetic susceptibility, and anhysteretic remanent magnetization to saturation isothermal remanent magnetization within specific ranges exhibited a positive correlation with Cd, Hg, and Sb. This research significantly advances our understanding of HMs risk assessment in lake sediments by leveraging accessible magnetic measurements within an interpretable machine learning framework.

Multistep magnetization switching in orthogonally twisted ferromagnetic monolayers.

The advent of twist engineering in two-dimensional crystals enables the design of van der Waals heterostructures with emergent properties. In the case of magnets, this approach can afford artificial antiferromagnets with tailored spin arrangements. Here we fabricate an orthogonally twisted bilayer by twisting two CrSBr ferromagnetic monolayers with an easy-axis in-plane spin anisotropy by 90°. The magnetotransport properties reveal multistep magnetization switching with a magnetic hysteresis opening, which is absent in the pristine case. By tuning the magnetic field, we modulate the remanent state and coercivity and select between hysteretic and non-hysteretic magnetoresistance scenarios. This complexity pinpoints spin anisotropy as a key aspect in twisted magnetic superlattices. Our results highlight control over the magnetic properties in van der Waals heterostructures, leading to a variety of field-induced phenomena and opening a fruitful playground for creating desired magnetic symmetries and manipulating non-collinear magnetic configurations.

Investigation on bio-synthesized Ni- and Al-doped cobalt ferrite using lemon juice as eco-fuel

Pure and doped cobalt ferrite (CoFe2O4) nanoparticles were prepared using sol-gel auto-combustion route with the aid of lemon juice as eco-fuel. In this study, Ni2+ and Al3+ ions were chosen as the dopants. The cubic spinel crystal structure of the synthesized ferrite samples was elucidated from the powder X-ray diffraction analysis. The crystallographic parameters associated with the samples were obtained from the Rietveld profile refinement of the diffraction patterns. The precise lattice parameter obtained from the Nelson-Riley extrapolation method is found nearly matches with the lattice parameter obtained from the Rietveld refinement of respective samples. The average crystallite size and microstrain accompanying with the samples were estimated from various methods such as via the Debye-Scherrer method, Williamson-Hall analysis and size-strain plot. By employing Tauc’s plot method, the optical parameters such as the direct bandgap, sub-bandgap and the Urbach energy of all the samples were calculated by analyzing the UV-Visible reflectance spectra. The room temperature magnetic properties of all the samples were estimated from the vibrating sample magnetometry. The nature of magnetic hysteresis revealed the semi-hard ferrimagnetism of the prepared cobalt ferrite samples. Also, the variation of magnetic properties with doping was analyzed. The weakening of interaction among the ions in tetrahedral and octahedral sites causes a decrease in the values of remanent magnetization, saturation magnetization and coercivity of doped samples.

Tuning the gas sensing properties of spinel ferrite NiFe2O4 nanoparticles by Cu doping

Copper substituted nickel ferrite nanoparticles (NiFe2O4) nanoparticles were prepared using hydrothermal technique at lower reaction temperature (175 °C). The structural, optical, dielectric, and magnetic properties were analyzed. The prepared nanopowders exhibited single phase-cubic spinel structure with a mean crystallite size in a narrow range 30–41 nm. Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed the presence of stretching vibration of metal oxide in the range 400–600 nm. Field Emission Scanning Electron Microscopy (FESEM) and High Resolution-Transmission Electron Microscopy (HR-TEM) observations showed non-uniform cuboidal shaped nano-sized particles. The chemical and oxidation state of the constituents were revealed by X-ray photoelectron spectroscopy (XPS) (Cu2+, Fe3+ and Ni2+). Mössbauer spectra manifested two sextet patterns attributed to tetrahedral (A) and octahedral (B) sites with a doublet pattern of low intensity. Magnetic measurement revealed the decrease of saturation magnetization (Ms) value and increase of remanence magnetization (Mr) and coercivity (Hc) values while doping. A higher specific capacitance was obtained for x = 0.5 (1417 F/g) with a pseudocapacitive behavior. At room temperature, Liquefied Petroleum Gas (LPG) showed high selective response (1300 s for 250 ppm) compared to other tested gases.

Magnetic Putty as a Reconfigurable, Recyclable, and Accessible Soft Robotic Material.

Magnetically hard materials are widely used to build soft magnetic robots, providing large magnetic force/torque and macrodomain programmability. However, their high magnetic coercivity often presents practical challenges when attempting to reconfigure magnetization patterns, requiring a large magnetic field or heating. In this study, magnetic putty is introduced as a magnetically hard and soft material with large remanence and low coercivity. It is shown that the magnetization of magnetic putty can be easily reoriented with maximum magnitude using an external field that is only one-tenth of its coercivity. Additionally, magnetic putty is a malleable, autonomous self-healing material that can be recycled and repurposed. The authors anticipate magnetic putty could provide a versatile and accessible tool for various magnetic robotics applications for fast prototyping and explorations for research and educational purposes.

Urban and suburban's airborne magnetic particles accumulated on Tillandsia capillaris

Air particle pollution is a current issue that can cause adverse problems to human health and the urban environment. A fraction of these emitted particles is magnetite and iron-rich materials, which may be accumulated by biological indicators and effectively characterized by environmental magnetism methods. Thus, we studied this emitted particle fraction using the epiphytic species Tillandsia capillaris growing in northwestern Argentina's urban, suburban, and rural areas. The accumulated airborne magnetic particles' properties revealed valuable information regarding potentially toxic elements, magnetic mineralogy, sizes, morphology, and concentration. Magnetite was detected in samples from all studied areas, and its remanent coercivity values (Hcr = 32.1–42.6 mT) in (sub)urban sites are similar to other reported cities in Latin America. The concentration of these airborne magnetic particles AMP varied between urban sites (mean and (s.d.) values of in situ magnetic susceptibility κis = 16.2 (9.4) × 10−6 SI, and specific magnetic susceptibility χ = 61.9 (31.4) × 10−8 m3 kg−1) and suburban sites (κis = 13.9 (9.9) × 10−6 SI, and χ = 43.9 (32.2) × 10−8 m3 kg−1), and it was distinctively higher than in clean sites. The spatial distribution of AMP was analyzed using a geostatistical model for the concentration-dependent magnetic parameter κis, which showed zones with high magnetic particle accumulation associated with vehicular traffic in the city and industrial emission in a suburban site. Among concentration-dependent magnetic parameters, the κis is recommended for magnetic biomonitoring because Tillandsia species' individuals are not processed for laboratory measurements, preserving them and allowing us the possibility of measurements over time.

Enhanced saturation magnetization in La3+ doped NiCo ferrites prepared by sol–gel auto-combustion method

Lanthanum doped nickel–cobalt nano ferrites with chemical formula Ni0.5Co0.5LaxFe2–xO4 (x = 0.05, 0.10, 0.15 and 0.20) were prepared using a simple sol–gel auto combustion method. The basic structural properties were determined by X-ray diffraction method and the formation of single phased spinel ferrite was confirmed. The crystalline size decreased from 25 to 11 nm and lattice parameter a increases with increase of La doping. The surface morphology of these ferrites was observed by field-emission scanning electron microscopy (FESEM) and agglomerated irregular grains are observed with increase of the rare earth element La doping. Energy-dispersive X-ray spectroscopy (EDX) result confirms the presence of the required elements. The Fourier transform infrared spectroscopy (FTIR) spectrum indicates the formation of the spinel ferrite structure with M−O bonds. Optical direct band measurements from ultraviolet–visible spectroscopy (UV-Vis) spectroscopy indicate that the direct band gap decreases from 1.39 to 1.19 eV for x = 0.05 to x = 0.15, then increases to 1.28 eV for x = 0.20. The room temperature magnetic properties of these ferrites were studied by a vibrating sample magnetometer (VSM). The enhanced saturation magnetization of 49.73 emu/g is observed for x = 0.10 and then saturation magnetizations are gradually decreased for x = 0.15 and x = 0.20. Interestingly the remanent magnetization and coercivity also follow the same trend.

A Strategy for Tuning the Structure, Morphology, and Magnetic Properties of MnFe2O4/SiO2 Ceramic Nanocomposites via Mono-, Di-, and Trivalent Metal Ion Doping and Annealing.

This work presents the effect of monovalent (Ag+, Na+), divalent (Ca2+, Cd2+), and trivalent (La3+) metal ion doping and annealing temperature (500, 800, and 1200 °C) on the structure, morphology, and magnetic properties of MnFe2O4/SiO2 ceramic nanocomposites synthesized via sol-gel method. Fourier-transform infrared spectroscopy confirms the embedding of undoped and doped MnFe2O4 nanoparticles in the SiO2 matrix at all annealing temperatures. In all cases, the X-ray diffraction (XRD) confirms the formation of MnFe2O4. In the case of undoped, di-, and trivalent metal-ion-doped gels annealed at 1200 °C, three crystalline phases (cristobalite, quartz, and tridymite) belonging to the SiO2 matrix are observed. Doping with mono- and trivalent ions enhances the nanocomposite's structure by forming single-phase MnFe2O4 at low annealing temperatures (500 and 800 °C), while doping with divalent ions and high annealing temperature (1200 °C) results in additional crystalline phases. Atomic force microscopy (AFM) reveals spherical ferrite particles coated by an amorphous layer. The AFM images showed spherical particles formed due to the thermal treatment. The structural parameters calculated by XRD (crystallite size, crystallinity, lattice constant, unit cell volume, hopping length, density, and porosity) and AFM (particle size, powder surface area, and thickness of coating layer), as well as the magnetic parameters (saturation magnetization, remanent magnetization, coercivity, and anisotropy constant), are contingent on the doping ion and annealing temperature. By doping, the saturation magnetization and magnetocrystalline anisotropy decrease for gels annealed at 800 °C, but increase for gels annealed at 1200 °C, while the remanent magnetization and coercivity decrease by doping at both annealing temperatures (800 and 1200 °C).