Low Coercivity Values Research Articles

Solvothermal Synthesis of SrFe12O19 Hexaferrites: Without Calcinations

In this study, the effect of temperature on the hydrothermal synthesis of single-phase SrFe12O19 hexaferrite (SrM) was investigated. For this synthesis, annealing or calcination process was applied. The Fe/Ba molar ratio was taken as 8:1. In this study, single-phase SrM NPs were synthesized via hydrothermal method. XRD patterns showed the presence of the hard (SrM) phase in the samples treated at 200 and 220 ∘C. Besides, formation of hexagonal plate-like samples was observed in SEM micrographs. Despite the low magnetization and coercive field values, the presence of the SrM phase was also shown in magnetization measurements. A reduced magnetization was explained by the existence of SrCO3 and Fe2O3 phases, and a high shape anisotropy is probably the reason of low coercivity.

Structural and magnetic properties of erbium doped nanocrystalline Li–Ni ferrites

A series of nanocrystalline Li0.25Ni0.5Fe2.25−xErxO4 (x=0.00, 0.02, 0.06, 0.08, and 0.10) ferrite powders, having a cubic spinel crystal structure and a low value of coercivity, was synthesized by the sol–gel auto-combustion route. The structure, morphology and magnetic properties of the prepared nanoferrites were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the magnetic property measurement system (MPMS). A well-defined single phase spinel structure is confirmed in all the samples by X-ray diffraction analysis. The lattice parameters of the samples increase slightly with increasing the erbium content. The crystallite size of the Er-doped samples is smaller than that of pure Li–Ni ferrite, and decrease regularly in the range of 36.0–14.5nm. It has been observed that the magnetic properties of these ferrites are strongly influenced by the added erbium content. The magnetic measurements indicate that saturation magnetization (Ms) and coercivity (Hc) decrease gradually with the increase of Er content in the lattice.

Structural, Electrical, and Magnetic Study of SrNi2+(Li1+Fe3+)0.5Fe16O27 Ferrite

W-type ferrite having chemical formula SrNi(LiFe)0.5Fe16O27 was prepared by using conventional solid state reaction method at little low temperature (1100°C). The prolonged and continuous heating resulted in better product formation and it has validated that the Lithium present in the compound facilitates the synthesis. Typical IR bands observed are assigned to the Fe–O bonds in S block of W ferrite structure and the band near 914.3 cm−1 is assigned to the stretching vibrations of Sr–O. High resistivity is found which suggested presence of very small amount of mixed valency cations on equivalent lattice apart from the little amount created due to the release of an electron by divalent Ni to become trivalent. The magnetic properties of compound do not differ much from those of the reported for SrNi2W ferrite except a little decrease in saturation magnetization at room temperature due to canting effect. The experimental observations support presumed site preferences to a greater extent and also the prediction that the Li present on 4fVI sub-lattice results in small canting effect of 12k cations. The low value of coercivity observed is attributed to the larger particle size resulting due to prolonged heating.

ONE POT SOLVOTHERMAL SYNTHESIS OF ORGANIC ACID COATED MAGNETIC IRON OXIDE NANOPARTICLES

In this work we present the synthesis and characterization of iron oxide nanoparticles (IONPs), which were structurally and magnetically characterized. The use of iron salts and an organic acid (l-serine or ascorbic acid) as precursors under solvothermal conditions yielded these coated IONPs. The powder X-ray diffraction pattern of FeO-1 and FeO-2 is consistent with hematite (a-Fe 2 O 3 ) and hematite-maghemite ((a-Fe 2 O 3 /g-Fe 2 O 3 ) respectively. The TEM analysis permits to estimate an average size of 10 nm for the FeO-1 sample. The magnetic characterization of the samples through the M(H) plots showed a very low coercivity value for both samples, being 53 Oe for FeO-1 and 10 Oe for FeO-2, indicating the very weak ferromagnetic character of the synthesized iron oxide species. Even though both organic acids under solvothermal conditions permit to obtain coated IONPs in one pot reaction, l-serine produces a more narrow-size distribution.

Thermal effect on magnetic properties of Mg-Zn ferrite nanoparticles

Magnesium–zinc ferrite (Mg0.5Zn0.5Fe2O4) powder was prepared by a solution combustion method using a mixture of sugar and urea as fuel. To understand the effect of size and crystallinity on its magnetic properties, combustion derived ferrite powder was subjected to calcination at different temperatures in an ambient atmosphere. The powder X-ray diffraction data of calcined samples was used to determine the effect of calcination on phase formation and crystallite size. The average crystallite size of single phase cubic spinel ferrite nanoparticles was found to increase with an increase in calcination temperature. Transmission electron microscopy images showed a uniform particle size distribution with average particle sizes varying in the range of 30–124nm. Magnetic properties were found to be affected by particle size; we observed a linear relationship between the saturation magnetization and particle size. Low values of squareness ratio and coercivity implied the superparamagnetic nature of the samples.

Characterization of magnetic NiFe nanoparticles with controlled bimetallic composition

The exploration of the magnetic properties of bimetallic alloy nanoparticles for various technological applications requires the ability to control the morphology, composition, and surface properties. In this report, we describe new findings of an investigation of the morphology and composition of NiFe alloy nanoparticles synthesized under controlled conditions. The controllability over the bimetallic composition has been demonstrated by the observation of an approximate linear relationship between the composition in the nanoparticles and in the synthetic feeding. The morphology of the NiFe nanoparticles is consistent with an fcc-type alloy, with the lattice strain increasing linearly with the iron content in the nanoparticles. The alloy nanoparticles exhibit remarkable resistance to air oxidation in comparison with Ni or Fe particles. The thermal stability and the magnetic properties of the as-synthesized alloy nanoparticles are shown to depend on the composition. The alloy nanoparticles have also be sown to display low saturation magnetization and coercivity values in comparison with the Ni nanoparticles, in line with the superparamagnetic characteristic. These findings have important implications for the design of stable and controllable magnetic nanoparticles for various technological applications.

Magnetic, ferromagnetic resonance and electrical transport study of Ni1−xTbxFe2O4 spinel ferrites

The impacts of terbium (Tb) contents on magnetic, ferromagnetic resonance (FMR), electrical and dielectric properties of Ni1−xTbxFe2O4 ferrites were investigated. A vibrating sample magnetometer was employed to probe the magnetic properties of the samples at room temperature. It was found that with the increased terbium content, the coercive force and saturation magnetization were decreased which may be attributed to spin canting. Magnetic dynamics of the samples were studied by ferromagnetic resonance in X band (9.5GHz) at room temperature. The incorporation of terbium sufficiently lowers the FMR line-width. The decrease in FMR line-width is attributed to the reduction of super-exchange interactions. The DC electrical resistivity and activation energy are higher for the substituted samples. The dielectric constant, dielectric loss (tanδ) and AC-conductivity decreased on account of doping. The decrease in dielectric constant is imputed to the reduction in the internal viscosity of the doped samples. The dielectric data are explained on the basis of space charge polarization. As Ni–Tb ferrites have low value of coercivity, high dielectric constant and low tanδ, they may be attractive for application in switching and memory storage devices.

Ultra-High-Frequency Behavior of BaFe$_{12}$O$_{19}$ Hexaferrite for LTCC Substrates

M-type barium hexaferrite (BaFe12O19) is investigated with an aim of using with low temperature co-fired ceramic (LTCC) substrate material. The as-calcined powders from combustion synthesis at neutral and acidic precursor solutions are used, which exhibit excellent properties of low coercive field values (up to 1350 Oe) and high magnetization (up to 60 emu/g). With an appropriate amount of Bi2O3 as sintering aid, high density ferrites have been realized at LTCC processing temperatures. The sintered ferrites possess bulk resistivity in excess of 109 Ω·cm, indicating their suitability for high-frequency applications. Complex magnetic permeability and magnetic loss factors are studied up to 1 GHz frequency. Complex permeability between 1.2 to 2.2 and magnetic loss tangent between 0.05-0.5 have been realized for the sintered ferrites. The influence of Bi2O3 content on resistivity and high-frequency magnetic properties is discussed. It is observed that the sample prepared by employing neutral pH during combustion preparation and calcined at 1200°C for 12 h shows low coercivity of 1350 Oe. After sintering at 900°C with 2 wt% Bi2O3, the sample shows better results with permeability of 1.5-1.7, magnetic loss tangent below 0.3 up to 700 MHz frequency and a high resonance frequency of 140 and 715 MHz in VHF and UHF band, respectively. Since the synthesis conditions provide better control over basic magnetic properties, the use of combustion synthesized BaFe12O19 material augers well for magnetic materials applications in LTCC technology.

Preparation of polyaniline/nickel oxide nanocomposites by liquid/liquid interfacial polymerization and evaluation of their electrical, electrochemical and magnetic properties

A novel route has been developed to synthesize polyaniline (PANI)/nickel oxide (NiO) nanocomposites via liquid/liquid interfacial polymerization where NiO and the initiator were dispersed in the aqueous phase and the monomer was dissolved in the organic phase. The synthesized samples were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet−visible absorption, X-ray diffraction, and electrochemical, electrical conductivity and magnetic property measurements. NiO was dispersed uniformly within the PANI matrix. The composites exhibited noticeable improvement in thermal stability and electrical conductivity in comparison with pure PANI. The composites showed excellent electrochemical reversibility at a scan rate of 0.1 V s−1 and good redox stability even up to 100 cycles. The room temperature magnetic hysteresis measurements show a low value of coercivity for the polymer composites in comparison with NiO. The remnant magnetization (Mr) values were found to be increased with increasing concentration of NiO in the composites. © 2013 Society of Chemical Industry

Effects of Sr-substitution on the structural and magnetic behavior of Ba-based Y-type hexagonal ferrites

Sr-substituted samples of Y-type hexagonal ferrites with chemical formula Ba2−xSrxNi2Fe12O22 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized using the sol–gel autocombustion method and were sintered at 1150 °C for 3 h. The samples were investigated by differential thermal and thermogravimetry analysis, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and vibrating sample magnetometry. X-ray diffraction analysis reveals that single phase samples can be achieved by substituting Sr2+ ions at Ba2+ sites in Y-type hexagonal ferrites. X-ray density and bulk density were observed to decrease whereas porosity increased with increasing Sr-concentration. All the samples show well defined hexagonal shape which is favorable for microwave absorbing purposes. The saturation magnetization values were calculated from M–H loops by the law of approach to saturation. The loops show low values of coercivity of a few hundred oersteds which is one of the necessary conditions for electromagnetic (EM) materials and is suitable for security, switching, sensing and high frequency applications.

Structural, infrared, magnetic and microwave absorption properties of rare earth doped X-type hexagonal nanoferrites

A series of Sr2−xNdxNi2 Fe28−yCoyO46 (x=0.02, 0.04, 0.06, 0.08, 0.10 and y=0.1, 0.2, 0.3, 0.4, 0.5) X-type hexagonal ferrites has been prepared by sol–gel method at 1250°C for 6h. XRD analysis shows the single phase of the prepared ferrites material. The lattice constant values and c/a ratio shows that the present assembled material belongs to the family X-type hexagonal ferrites. The peaks in the FTIR spectra are the characteristics of the hexagonal ferrites. The crystallite size measured by Scherer formula is in good agreement with the crystallite size measured by TEM and HRTEM. The enhancement in the magnetic properties can easily be observed with the doping of rare earth element Nd3+ and divalent Co2+. Due to high saturation and low coercivity values the present material can be good microwave absorber. The temperature dependent saturation and remanance magnetization decreases monotonically with temperature. The minimum value of reflection loss enhances with the substituent and the attenuation constant results are in agreement with reflection loss results.

Extraordinary magnetization of amorphous TbDyFe films

A study of the magnetic properties and their relationship with the magnetoelastic properties of amorphous (Tb0.3Dy0.7)40Fe60 films prepared by dc magnetron sputtering is presented. The magnetostrictive coefficient λ reaches values up to 300ppm in a field of 0.1T. At low temperatures the films present spin-glass behavior with Tf≅160K. At room temperature the films show low coercivity values, less than 30mT, whereas at temperatures below 40K huge coercivities are observed which reach values up to 2.5T at 5K.

Enhanced ferroelectricity and magnetoelectricity in 0.75BaTiO3-0.25BaFe12O19 by spark plasma sintering

Spark Plasma Sintering (SPS) technique was employed to synthesize 0.75BaTiO3-0.25BaFe12O19 composite. X-ray diffraction studies revealed that the composite consisted of both BaTiO3 (ferroelectric phase) and BaFe12O19 (ferrimagnetic phase), respectively. The SPS treated sample showed improved ferroelectric nature when compared to conventional sintered (CS) sample. Transformation from hard to soft magnetic nature was envisaged by magnetization measurements for SPS sample. A slim hysteresis loop was recorded with a low coercivity values (390 Oe) when compared to CS sample (3900 Oe). Mossbauer spectroscopy analysis indicated that the existence of a partial amount of ?-Fe2O3 phase in the lattice, giving rise to soft magnetic nature. The SPS sample showed slightly higher value of magnetoelectric output of 2.95 mV/cm at 3 kOe magnetic field when compared to the CS sample (1.45 mV/cm at 3 kOe). The present investigation compares the spark plasma sintered sample with the conventional sintered sample.

Phase States in Multicomponent PZT-Based Materials Depending on Poling Conditions

Phase states of the PZT-based multicomponent solid solutions belonging to the rhombohedral area of the phase х-Т diagram with low coercive field values are considered. The solid-solution samples in the initial state are proved to be heterophase (R3c and P4mm mixtures) and reveal relaxor properties. The anomalies of dielectric characteristics obtained in poled samples are due to the R3c→R3m phase transition. The manifestations of relaxor properties above the temperature of the dielectric permittivity maximum are caused by the R3m phase in the P4mm and Pm3m phase mixture.

One-pot hydrothermal synthesis and magnetic properties of octahedral and clover-structured Fe3O4 by a Ce cation-assisted route

Magnetite Fe3O4 particles with octahedrons and clover-structures were synthesized by a facile one-pot hydrothermal method using a cerium cation-assisted route. After hydrothermal reaction at 180°C, the crystalline structure, composition and morphologies of the products were confirmed by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and scanning electron microscopy (SEM), respectively. The results showed that the structure and morphology of the products can be tuned by altering the concentration of Ce(NO3)3 in the precursor solution. Furthermore, the magnetic performances of the products were evaluated on a vibrating sample magnetometer at room temperature. Magnetic studies reveal that the product with mixed structure of octahedrons and clover-structures exhibits high saturation magnetization with 89emu/g and very low coercivity value with 33Oe.

Soft Magnetic Properties of Electrodeposited Fe-Ni Films Prepared in Citric Acid Based Bath

Electrodeposited Fe-Ni films are widely used in device applications. However, there is a growing awareness of the toxicity of the plating bath containing boric acid. In order to avoid boric acid in the deposition process, we have employed a citric acid based bath for electrodeposition of Fe-Ni films and investigated the effect of the acid content in the bath on the structural and magnetic properties of the deposited films. It is found that the Fe content of the film depends largely on the acid concentration and low coercivity values of less than 30 A/m are realized when the Fe content of the film is around 22 at.%. This magnetic softness is attainable in a wide film thickness range between 20 and 120 μm. Our process exhibits a relatively high cathode efficiency of above 55%. Furthermore, a high deposition rate of 170 μm/h is obtained without sacrificing the magnetic softness of the film by increasing the current density during the deposition. From these results, we conclude that the citric acid based bath is an environmentally friendlier plating bath ideal for mass-production of magnetically soft Fe-Ni films.

Giant magnetoimpedance in thin amorphous wires: From manipulation of magnetic field dependence to industrial applications

Abstract We present the results on tailoring of soft magnetic properties and GMI effect in thin microwires paying special attention on achievement of low hysteretic high GMI effect in the extended frequency range (up to 4 GHz). We observed considerable dependence of the GMI ratio and magnetic anisotropy field, Hk, of Co-rich amorphous microwires with vanishing magnetostriction constant on the internal and applied stresses. For low magnetostrictive Co-rich composition we obtained microwires low coercivity values (generally below 10 A/m). Field dependence of the off-diagonal voltage response measured in pulsed regime (pulsed GMI) exhibits anti-symmetrical shape. The magnetic anisotropy of Co and Fe-rich microwires can be tailored by stress or magnetic field annealing. Particularly stress annealed Fe-rich microwires exhibit stress-sensitive GMI effect and hysteretic properties. Varying the time and the temperature of such stress annealing we are able to tailor both magnetic properties and GMI. Additionally, magnetic response of linear microwires arrays and GMI effect of the system containing few microwires can be tailored through the magnetostatic interaction between the microwires. We found, that if the surface anisotropy is not circumferential, then the MI curve Z(H) presents hysteresis. This hysteresis can be suppressed by application of sufficiently high DC bias current IB that creates a circumferential bias field HB.

Effect of divalent cation substitution in the magnetoplumbite structured BaFe12O19 system

Synthesis of magnetically ordered barium hexaferrite powders and the adjustment of magnetic properties for perpendicular magnetic recording media are realized through substitution of divalent cation (Ca) in the BaFe12O19 system. The Ca2+ substituted Ba1−xCaxFe12O19 (where x = 0.05, 0.1, 0.15 and 0.2) compounds have been prepared through solid state reaction technique. The powder X-ray diffraction analysis reveals that all the prepared compounds crystallized in magnetoplumbite hexagonal structure and the flat hexagonal platelet morphology of the crystallites was identified through scanning electron microscopy. The formation of magnetoplumbite structured Ba1−xCaxFe12O19 system due to mechanical activation was supported by micro-Raman measurements. Both pure and Ca substituted BaFe12O19 compounds exhibit sharp intense peaks which reveals defect free environment in the crystal lattice. From the room temperature magnetization studies, it was observed that the saturation magnetization (MS) and remanent magnetization (MR) values drastically decreases for the Ba0.95Ca0.05Fe12O19 compound which may be due to the existence of spin canting effect and leads to the reduction of super exchange fields. The increase in MS and MR values for the Ba0.9Ca0.1Fe12O19 and Ba0.85Ca0.15Fe12O19 compounds could be attributed to the enhanced hyperfine fields at 12k and 2b sites due to the strengthening of Fe3+–O–Fe3+ super exchange interactions. A large reduction in the coercivity value from 3,090 to 1,548 Gauss may be attributed to the fall in magneto crystalline anisotropy. The high temperature magnetization studies infer that while increasing substitution level of Ca in the BaFe12O19 system results in decreasing trend in Curie temperature. The room temperature dielectric measurement shows that the incorporation of Ca2+ in the BaFe12O19 system results with increase in the dielectric constant and this case substantiates the space charge polarization. The magnetically ordered BaFe particulate having higher saturation and low coercivity values with superior magnetic and dielectric behaviour exhibiting the possibility for future high-recording-density storage products.

Soft magnetic properties of MnZn ferrites prepared by powder injection moulding

In this study, properties of soft-magnetic manganese zinc ferrite manufactured by powder injection moulding - PIM technology were presented. A powder consisting of Mn1- xZnxFe2O4 with small addition of hematite ?-Fe2O3 was mixed with an organic binder (wax and thermoplastic) to form ferrite feedstock. The ferrite feedstock was injected in a mould with a cavity shaped like a small cylinder with a hole on the main axis. Injection moulded samples were then solvent, thermally debinded and sintered in air atmosphere. Structure of sintered sample was characterized using X-ray diffractometry, scanning electron microscopy and thermomagnetic measurements. Magnetic properties were measured by hysteresis graph at different frequencies up to 1 kHz. Sintered sample contains a mixture of two phases Mn0.6Zn0.4Fe2O4 (68 wt. %) and ?-Fe2O3 (32 wt. %). The Curie temperature is TC ? 220?C for the green sample but after the heating up to 470?C, TC increase up to about 300?C. The high increase of normalized magnetic permeability of about 800 % was observed due to melting and burning of binder. The hysteresis loop of sintered MnZn ferrite toroidal cores has an R-shape with saturation of 0.44 T and remanence ratio of 0.49. The low value of coercivity (only 47 A/m) was related to the presence of ?-Fe2O3 crystalline phase and attained already optimum density (? ? 4.8 g/cm?) i.e. observed low level of porosity. Attained relative magnetic permeability ?r ? 2000 as well as power losses Ps ? 21 W/kg for sintered sample (at 1 kHz; 0.39 T) is in agreement with the MnZn ferrite commercial samples.

Oligo(ω-pentadecalactone) decorated magnetic nanoparticles

Hybrid magnetic nanoparticles (mgNP) with a magnetite core diameter of 10 ± 1 nm surface functionalized with oligo(ω-pentadecalactone) (OPDL) oligomers with Mn between 1300 and 3300 g mol−1 could be successfully prepared having OPDL grafted from 200 mg g−1 to 2170 mg g−1. The particles are dispersible in chloroform resulting in stable suspensions. Magnetic response against an external magnetic field proved the superparamagnetic nature of the particles with a low coercivity (Bc) value of 297 µT. The combination of the advantageous superparamagnetism of the mgNP with the exceptional stability of OPDL makes these novel hybrid mgNP promising candidates as multifunctional building blocks for magnetic nanocomposites with tunable physical properties.