Size Controlled Synthesis of CoFe2O4 Nanoparticles with Polyethylene Glycol

Nanoparticles (NPs) of CoFe₂O₄, which is a well-known spinel ferrite and hard magnetic material with very high cubic magnetocrystalline anisotropy, were synthesized by co-precipitation method. The effect of different molecular weights of polyethyleneglycol (PEG) on the magnetic properties and crystallite size of CoFe₂O₄ NPs was investigated by using PEG-400, PEG-10.000 and, PEG-20.000. Crystalline structure and size of CoFe₂O₄ NPs were studied using X-ray diffraction (XRD). The VSM studies showed that the saturation magnetization (M _s ) and coercivity (H _c ) of the CoFe₂O₄ NPs depend on molecular weight of PEG.     

Temperature dependence on the mass susceptibility and mass magnetization of superparamagnetic Mn–Zn–ferrite nanoparticles as contrast agents for magnetic imaging of oil and gas reservoirs

The mass susceptibility (χ_mass) and mass magnetization (M_mass) were determined for a series of ternary manganese and zinc ferrite nanoparticles (Mn–Zn ferrite NPs, Mn_xZn_1?xFe₂O₄) with different Mn:Zn ratios (0.08 ≤ x ≤ 4.67), prepared by the thermal decomposition reaction of the appropriate metal acetylacetonate complexes, and for the binary homologs (M_xFe_3?xO₄, where M = Mn or Zn). Alteration of the Mn:Zn ratio in Mn–Zn ferrite NPs does not significantly affect the particle size. At room temperature and low applied field strength the mass susceptibility increases sharply as the Mn:Zn ratio increases, but above a ratio of 0.4 further increase in the amount of manganese results in the mass susceptibility decreasing slightly, reaching a plateau above Mn:Zn ≈ 2. The compositional dependence of the mass magnetization shows less of a variation at room temperature and high applied fields. The temperature dependence of the mass magnetization of Mn–Zn ferrite NPs is significantly less for Mn-rich compositions making them more suitable for downhole imaging at higher temperatures (>100 °C). For non-shale reservoirs, replacement of nMag by Mn-rich Mn–Zn ferrites will allow for significant signal-to-noise enhancement of 6.5× over NP magnetite.     

Interplay Between Surface Effects and the Magnetic Properties in Polycrystalline Superconductors

The effects of the grain boundaries on the magnetic properties are studied in the polycrystalline superconductors. The interaction of the Abrikosov vortex with both the surface and Josephson junction as well as with other vortices and applied magnetic field are taken into account in this study by the London theory approach. It is shown that the magnetic behavior is strongly dependent of the anisotropy ratio as well as the normalized grain size and the coupling parameter between the grains. The first flux entry field H _p , the lower critical field H _{c 1} and the Gibbs free energy are computed. The vortex–vortex interaction and magnetization M(H) are also investigated.     

Rapid synthesis of nano-magnetite by thermal plasma route and its magnetic properties

Thermal plasma method has been used to process mild steel scrap for nanopowder synthesis by changing the operating current. The phase analysis of the product nanopowders was studied by X-ray diffraction and the chemical composition was studied by energy dispersive spectroscopy. The morphology, particle size and particle size distribution of the samples were investigated by field emission scanning electron microscope. In addition to the above, the magnetic properties of the samples were investigated by superconducting quantum interface device magnetometer and high temperature vibrating sample magnetometer (HTVSM). From this study, the results indicate that the processed nanopowders were magnetite and exhibit spherical morphology. The magnetic properties, such as, saturation magnetization (M_S), coercivity (H_C), and Curie temperature (T_c) were estimated. The M–H loops exhibited soft magnetism and samples corresponding to 60 and 70A showed the highest M_S and H_C, respectively. The Curie temperature was determined for the sample corresponding to 60A using HTVSM as 852 and 840?K from the heating and cooling curves, respectively. The outcome of the results suggests that thermal plasma is a contaminant-free process and is suitable for processing metal scrap.     

Self-propagating high temperature synthesis and magnetic properties of Ni0.35Zn0.65Fe2O4 powders

Ni-Zn ferrite powders were synthesized by self-propagating high temperature synthesis (SHS) method. X-ray diffraction, TEM and vibrating sample magnetometry (VSM) were used to characterize the phase composition, microstructure and magnetic properties of the combustion products. The effect of the combustion temperature (T _c), the major parameter of the SHS process, on particle size, phase composition and magnetic properties of the products was also studied. The results showed that particle size grew with the increasing combustion temperature. The maximum saturation magnetization,M _s, increased with combustion temperature indicating the growth of grain size and high degree of ferritization, while residual magnetization,M _r, and coercive force,H _c, decreased. Compared with other methods, Ni_0.35Zn_0.65Fe₂O₄ ferrite powders with improved magnetic properties can be obtained by SHS at 1000°C.     

Enhanced room temperature multiferroic behaviour of Ni-doped Na0.5Bi0.5TiO3 ceramics

In this paper, room temperature multiferroic behaviour in Ni (Nickel)-doped NBT (Na_0.5Bi_0.5TiO₃) ceramics synthesized using solid state reaction technique have been investigated. Structural, dielectric, ferroelectric, magnetic and magneto-dielectric properties were consistently probed with the increment in transition metal doping. XRD peaks were indexed for the monoclinic Cc phase. SEM micrographs clearly depicted the reduction of grain size with addition of Ni content. Ferroelectric polarization (P) vs applied electric field (E) hysteresis curves shows an increase in lossy behaviour with an increase in Ni content. The room temperature magnetization (M) vs applied magnetic field (H) curves depict the weak ferromagnetic ordering on increasing the Ni doping. Enhanced magneto-dielectric change of 1.26% was observed in 25% Ni-doped NBT ceramic, which may be useful in the development of novel non-volatile lead-free multiferroic memory devices.

     

Thermophysical and Magnetic Properties of Carbon Beads Containing Nickel Nanocrystallites

Ferromagnetic and superparamagnetic nickel nanocrystallites, stabilized in a carbon matrix, were prepared by a three-step procedure including formation of a Ni acrylamide complex, followed by frontal polymerization and pyrolysis of the polymer at various temperatures. It was found that the procedure applied enables fabrication of magnetic beads containing metallic nanocrystallites embedded in a carbon matrix. The size of the crystallites, their morphology, volume fraction, and magnetic properties can be tailored by the pyrolysis temperature. The size of the crystallites affects their behavior in an external magnetic field, i.e., a heating process is the most effective for a sample pyrolyzed at 873 K. The revealed H ⁿ-type dependence of the temperature increase rate, (dT/dt) _t=0, on the amplitude of the magnetic field indicates the presence of both superparamagnetic and ferromagnetic particles in all the samples studied since n > 2. For the superparamagnetic particles, the heating mechanism is associated with Néel relaxation. For the lower values of the magnetic field amplitude, H <  H ₀, the relaxation losses dominate whereas for the opposite case, H >  H ₀, the magnetic hysteresis is the main source of thermal energy losses. The composites containing magnetic Ni nanocrystallites entrapped in a carbon matrix can be potentially applied for hyperthermia treatment.     

Cobalt ferrite nanoparticles in a mesoporous silicon dioxide matrix

We have studied magnetic nanoparticles of cobalt ferrite obtained by the extraction-pyrolysis method in a mesoporous silicon dioxide (MSM-41) molecular sieve matrix. The X-ray diffraction data show evidence for the formation of CoFe₂O₄ particles with a coherent scattering domain size of ∼40 nm. Measurements of the magnetization curves showed that powders consisting of these nanoparticles are magnetically hard materials with a coercive field of H _c(4.2 K) = 9.0 kOe and H _c(300 K) = 1.8 kOe and a reduced remanent magnetization of M _r/M _s(4.2 K) = 0.83 and M _r/M _s(300 K) = 0.49. The shape of the low-temperature (4.2 K) magnetization curves is adequately described in terms of the Stoner-Wohlfarth model for randomly oriented single-domain particles with a cubic magnetic anisotropy.     

High-frequency magnetic properties of Ni-Zn ferrite nanoparticles synthesized by a low temperature chemical method

Spinel-structured Ni-Zn ferrite nanoparticles (NPs) have been directly synthesized by a low temperature co-precipitation method. The structure and high-frequency magnetic properties of the particles were investigated. The as-prepared Ni-Zn ferrite NPs demonstrate typical soft magnetic properties. The saturation magnetization (M_s), as high as about 60 emu/g, was achieved. The imaginary part μ^' ' of the permeability shows a broad peak in the frequency range 200 MHz~6 GHz, which indicates that the as-prepared Ni-Zn ferrite NPs have a remarkable feature of electromagnetic (EM) wave absorption in the high-frequency range. Hence, resultant Ni-Zn ferrite NPs can be used as efficient microwave absorbers and effective heating mediators for hyperthermia application in cancer therapy.     

Nickel Promoted Palladium Nanoparticles for Electrocatalysis of Carbohydrazide Oxidation Reaction

Carbohydrazide is a potential alternative to toxic hydrazine for fuel cell applications to overcome the challenges of storage and transportation of hydrogen. In this work, Ni‐alloyed Pd nanoparticles (NPs) with varied Pd–Ni ratios supported on carbon black (PdNi_x/C) are prepared and their catalytic performance for the carbohydrazide electro‐oxidation reaction is investigated. The catalytic performance of PdNi_x/C NPs is significantly improved in comparison to Pd/C NPs. The current density of PdNi_x/C NPs with optimized Pd–Ni atom ratio can reach 3.26 A mg^?1_metal at a potential of 0.4 V (vs reversible hydrogen electrode), which is an increase of 2.4 times compared to that of Pd/C. The density functional theory calculation indicates the enhanced catalytic activity is caused by the change of adsorption energy of carbohydrazide molecules on the metal surface. It exhibits a volcano relationship between the adsorption energy and the catalytic current density of PdNi_x/C with varied Pd–Ni atom ratios.     

Magnetization of EuS–PbS Multilayers with Antiferromagnetic Interlayer Coupling

SQUID magnetometry is applied to study the temperature and magnetic field dependence of magnetization M(T, H) of semiconductor EuS–PbS ferromagnetic multilayers grown on insulating KCl(100) and conducting n-PbS(100) monocrystalline substrates. For low external magnetic fields (of the order of 10 Oe) and PbS spacer layers thinner than about 2 nm, we observe in EuS–PbS–EuS trilayers the strongly nonmonotonic temperature dependence of magnetization with almost zero total magnetic moment below the Curie temperature. The application of the magnetic field of the order of 100 Oe restores the regular monotonic increase of magnetization with decreasing temperature. To explain this M(T,H) dependence we present a model that considers the competition of three (temperature dependent) contributions to the total magnetic energy of the trilayer: the antiferromagnetic interlayer interaction energy, the Zeeman energy, and the energy of in-plane magnetocrystalline anisotropy.     

Reagent control over the composition of mixed metal oxide nanoparticles

Binary (M¹ ? M² ? O) and ternary (M¹ ? M² ? M³ ? O) metal-oxide nanoparticles (NPs) have been prepared by thermal decomposition in benzyl ether of the appropriate M(acac)_n (M = Fe, Mn, Pd, Cu, Al, Gd) compounds in the presence of a mixture of oleic acid and oleylamine templating (surface capping) ligands, and 1,2-hexadecanediol as an accelerating agent. The metal percentage and the particle size were investigated as a function of the starting composition. The NP composition is controlled by the relative reaction rates of the particular precursors, such that prediction of NP composition from reagent ratios is not straightforward. However, understanding reaction rate limitations allows for alternative synthesis to be developed. In some cases, ligand exchange reaction and subsequent decomposition are possibly more important than thermal decomposition.     

Synthesis, Structural, Electrical, Magnetic Curie Temperature and Y–K Angle Studies of Mn–Cu–Ni Mixed Spinel Nanoferrites

Nanoferrites of composition Mn_0.50Cu_0.5−x Ni _x Fe₂O₄ (0.00≤x≤0.50) are prepared by chemical coprecipitation method. The prepared nano-ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), two probe resistivity apparatus, and vibrating sample magnetometer (VSM) to study the compositional, structural, morphological, electrical, and magnetic properties with varying concentration (x) in the composition of the prepared nanoferrites. XRD confirmed formation of single phase spinel ferrite with crystalline size in the range of 16–29 nm. The lattice parameter (a) decreases with a decrease of Cu concentration. Further information about the structure and morphology of the nanoferrites was obtained from SEM and results are in good agreement with XRD. FTIR gives information about distribution of cations and anions by confirming the presence of high and low frequency bands due to tetrahedral and octahedral sites, respectively. The electric properties were measured and analyzed by using homemade two probe resistivity apparatus showing semiconducting behavior of synthesized ferrites. The magnetic hysteresis curves clearly indicate the soft nature of the prepared samples. Various magnetic parameters such as saturation magnetization (M _s), and remanence (M _r) are calculated from the hysteresis loops and observed compositional dependent. Saturation magnetization and magnetic moment increase with Ni content. This is due to the existence of localized canted spin. Coercivity and M _s decreases while Y–K angles increase with Cu²⁺ content. The Ni²⁺ addition improves the magnetic properties. Curie temperature decreases with increase in Cu contents.     

Effect of annealing parameters on the magnetic properties of NiZn ferrite thin films

Ni_0.5Zn_0.5Fe_2.0O_4.0 thin films (NZFs) were deposited on Si (100) substrate by a sol–gel method, and the effects of annealing parameters on the structure and magnetic properties of the proposed films were investigated. Moderate heating rate was beneficial to the nucleation of NZFs. When the heating rate was 2 °C/min the saturation magnetization (M _s) achieved its maximum and the coercivity (H _c) reached its minimum. Both the crystallization and M _s of NZFs enhanced with increasing annealing time; however, H _c changed contrarily. High quenching temperature produced a large stress and consequently deteriorated magnetic properties. The optimal annealing parameters of NZFs were annealed at 700 °C, heating rate 2 °C/min, annealing time 1 h, and gradually cooled to room temperature. Finally, NZFs showed a high magnetization of 320 emu/cm³ and low coercivity of 86 Oe.     

Synthesis, Structural, and Magnetic Characterization of Mn1?x Ni x Fe2O4 Spinel Nanoferrites

Nanoferrites of composition Mn_1−x Ni _x Fe₂O₄ with x=0.00, 0.25, 0.50, 0.75, 1.00 were prepared by the chemical coprecipitation method. The prepared nanoferrites were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) and vibrating sample magnetometer (VSM) to study the compositional, structural, morphological and magnetic changes taking place with varying Ni concentration in the composition of the prepared nanoferrites. IR reveals the presence of both high-frequency and low-frequency bands due to tetrahedral and octahedral sites, respectively. The XRD results indicated the formation of single spinel ferrite with crystalline size in the range of 14–26 nm. The lattice parameters (a) decrease with the increase of the Ni concentration x in the lattice. Further information about the morphology of the nanoferrites was obtained from the AFM and SEM results. The magnetic hysteresis curves clearly indicate the soft nature of the prepared nanoferrites. Various magnetic properties such as saturation magnetization (M _s ) and remanence (M _r ) are calculated from the hysteresis loops and observed to be dependent on the composition.     

Effect of heating rate on the microstructural and magnetic properties of nanocrystalline Fe<Subscript>81</Subscript>Si<Subscript>4</Subscript>B<Subscript>12</Subscript>P<Subscript>2</Subscript>Cu<Subscript>1</Subscript> alloys

The effect of heating rate on the structural and magnetic properties of the nanocrystalline Fe₈₁Si₄B₁₂P₂Cu₁ alloy has been investigated. Amorphous Fe₈₁Si₄B₁₂P₂Cu₁ alloy was annealed at 753 K for 180 s at different heating rates ranging from 0.05 to 5 K/s in protective argon atmosphere. The structural and magnetic properties of the as-quenched and annealed alloys were studied using X-ray diffractometer (XRD), differential scanning calorimeter (DSC), vibrating sample magnetometer (VSM), and B–H loop tracer, respectively. Amorphous precursor prepared by industry-grade raw materials is obtained. The increase of heating rate is found to be significantly effective in decreasing the grain size of α-Fe(Si) phase, but the grain size increases at higher heating rate. The volume fraction of α-Fe(Si) phase shows a monotonic decrease with the increase of the heating rate. The coercivity H _c markedly decreases with increasing heating rate and exhibits a minimum at the heating rate of 0.5 K/s, while the saturation magnetization, M _s, shows a slight decrease. These results suggest that the effect of heating rate on H _c and M _s is originated from the changes of grain size and the volume fraction of α-Fe(Si) phase.     

Studies on magnetic and magnetoelectric properties of the NiFe2O4–Ba0.7Sr0.3TiO3 composites

The magnetic and magnetoelectric properties of magnetoelectric (ME) composites consisting of with nickel ferrite (NiFe₂O₄) and barium strontium titanate (Ba_0.7Sr_0.3TiO₃) were investigated. The composites were prepared by standard double sintering ceramic method. The X-ray diffraction analysis was carried out to confirm the phases formed during sintering and also to calculate the lattice parameters. The hysteresis measurements were done to determine saturation magnetization (M_s), remenance magnetization (M_r) and coercivity (H_c) of the samples. The magnetoelectric voltage coefficient (dE/dH)_H was studied as a function of intensity of the magnetic field. The measured magnetoelectric (ME) response demonstrated strong dependence on the volume fraction of NiFe₂O₄ and the applied magnetic field. A large ME voltage coefficient of about 560 μVcm⁻¹Oe⁻¹ was observed for 15% NiFe₂O₄ + 85% Ba_0.7Sr_0.3TiO₃ composite.     

Magnetization Processes of (La0.7Pb0.3MnO3)1?x(SiO2)x Composites

The ceramic composites, (La_0.7Pb_0.3MnO₃)_1−x (SiO₂) _x , with diluted magnetic properties are prepared using solid-sate sintering route. Magnetization processes of (La_0.7Pb_0.3MnO₃)_1−x (SiO₂) _x composites are explored in this study. Ferromagnetism is gradually attenuated due to the magnetic dilution induced by the increase of SiO₂ content. Clearly, irreversible behavior is observed in the zero-field cooling and the field cooling (ZFC–FC) curves at a low field of 100 Oe. Saturation magnetization decreases as x increases while ferromagnetic transition temperature remains around 346 K for all composites. All the composites exhibit ferromagnetic hysteresis behavior which can be modeled by the law of the approach to saturation in the form M=M _S(1−a/H). The term a/H expresses the deviation of magnetization from saturation. The smaller factor a for La_0.7Pb_0.3MnO₃-rich samples results in sharper square curve which should be associated with the long-range spin order of ferromagnetic coupling.     

A facile route to sonochemical synthesis of magnetic iron oxide (Fe3O4) nanoparticles

A facile sonochemical approach was applied for the large scale synthesis of iron oxide magnetic nanoparticles (NPs) using inexpensive and non-toxic metal salts as reactants. The as-prepared magnetic iron oxide NPs has been characterized by XRD, TEM, EDS, and VSM. X-ray diffraction (XRD) and EDS analysis revealed that Fe₃O₄ NPs have been successfully synthesized in a single reaction by this simple method. Transmission electron microscopy (TEM) data demonstrated that the particles were narrow range in size distribution with 11 nm average particle size. Moreover, TEM measurements also show that the synthesized nanoparticles are almost spherical in shape. The magnetization curve from vibrating sample magnetometer (VSM) measurement shows that as-synthesized NPs were nearly superparamagnetic in magnetic properties with very low coercivity, and magnetization values were 80 emu/g, which is very near to the bulk value of iron oxide. The estimated value of mass susceptibility of as-synthesized nanoparticles is Xg = 5.71 × 10^− 4 m³/kg.     

The hysteresis loops of magnetic ferrites and the processes involved in their formation

It is shown that a specimen's microstructure affects the form of its magnetization curves but notM _s, the saturation magnetic moment per cm³ norH _s, the applied field strength required for saturation. A procedure is then given for the precise determination ofM _s andH _s using data derived from the hysteresis loops of polycrystalline isotropic specimens. The procedure is simple to use and avoids the laborious extrapolation requirements of the “law of approach”. Finally, the magnetization processes involved in forming the hysteresis loops betweenH _s and —H _s are described.