Saturation Magnetization Field Research Articles

Effect of Mn substitution on structural and magnetic properties of cobalt ferrite

Manganese substituted Cobalt Ferrite Co1-xMnxFe2O4() nanoparticles were prepared using low temperature chemical co-precipitation method. All the samples were annealed at 900°C for 3 hours. The crystal lattice symmetry and phase purity were performed by X-ray diffraction (XRD). The varying dopent concentration affects the crystalline size, surface morphology and magnetic properties of the cobalt ferrite. The particle sizes are found to be in the range of 29-37 nm. SEM with EDAX examines the morphological and compositional analysis of the nanoparticles. EDAX confirms the presence of Co, Mn, Fe and O. Fourier transform infrared spectroscopy (FTIR) study confirms the formation of spinel ferrite. The saturation magnetization, magnetic remanence and coercive field of CoMn nanoparticles are obtained at room temperature. Saturation magnetization initially increases and then decreases for higher value of dopent, which shows applicability of these materials for recording media and magnetic data storage. Copyright © 2017 VBRI Press.

High-Frequency Motor Modeling by Harmonic Magnetic Field Analysis Considering Magnetic Saturation and DC Bias Magnetic Field

High-Frequency Motor Modeling by Harmonic Magnetic Field Analysis Considering Magnetic Saturation and DC Bias Magnetic Field

Synthesis and Characterization of Spinel Ferrite Co0.8Fe2.2O4 Nanoparticle

Cobalt ferrite Co0.8Fe2.2O4 nanoparticles were prepared using the sol-gel auto combustion process. The effects of calcination temperature on structural, magnetic, and electrical properties were studied. The cubic spinel phase fashioning of ferrite structure was confirmed using Fourier Transform-Infrared Spectroscopy (FT-IR) and X-ray Diffraction Patterns (XRD). The size of the formed crystallite of ferrite samples is ranged from 24.530 to 49.067 nm and it is found to be dependent on calcination. According to the images, which were taken by a Field Emission-Scanning Electron Microscope (FE-SEM), the particle size increases with raising the calcination temperature. Energy Dispersive Spectrum (EDS) was used to confirm the presence of Co, Fe, and O in all samples. A Vibrating Sample Magnetometer (VSM) was used to study the magnetic properties such as coercivity, saturation magnetization, and remanence field for the as-burnt and calcined samples. All samples exhibited ferrimagnetic behavior. As the calcination temperature rises, saturation magnetization (M_s), remanent magnetization (M_r), and squareness ratio (M_r/ M_s) increased. This behavior is related to the spin canting and disturbance in the surface spin. At room temperature, the dielectric loss factor (ε''), dielectric loss angle (tanδ), dielectric constant (ε'), and the conductivity σ_ac of all samples were examined as a function of frequency using the LCR meter. The changes in dielectric properties have been characterized at frequencies ranged from 50Hz to 2MHz based on Koop's theory, Maxwell-Wagner polarization, and electron hopping. As frequency rose, all-dielectric properties exhibited natural behavior.

DC and AC tunneling magnetoelectric responses of cobalt lateral nanogranular films

We demonstrate a new structural optimization of cobalt–(barium fluoride) lateral nanogranular films, achieving independently variable direct current (DC) and alternating current (AC) tunneling effects, in the film plane and out of the plane, respectively. Lateral nanogranular films were successfully fabricated via programmable tandem sputtering. Flat-shaped magnetic Co nanogranules were periodically inserted between dielectric barium fluoride layers of different thicknesses. All the lateral nanogranular films were insulating, with electrical resistivities ρ exceeding 1013 μΩ·cm, even with a Co content as high as 30 at.%. A lateral tunneling magnetoresistance (TMR) effect and vertical tunneling magnetodielectric (TMD) effect were found in the same lateral nanogranular film with 30 at.% Co. For a nanogranular film with lateral Co nanoparticles, the sensitivity of both the TMR and TMD ratio were improved at small magnetic fields compared with conventional films with spherical Co nanoparticles, reflecting its small saturation magnetic field. This layer-ordered metal–insulator nanogranular structure has potential applications in AC/DC hybrid elements as a high-sensitivity magnetic sensor.

Magnetic Field Saturation of Non-Insulation High-Temperature Superconducting Coils during Overcurrent

Non-insulation high-temperature superconducting coils provide a much lower risk of burnout in fault/abnormal conditions, such as hot-spot quench and overcurrent. This study employs an equivalent circuit grid model, coupled with magnetic field calculation and the E–J power law of superconductors, to deeply and systematically investigate the overcurrent charging process in a double-pancake non-insulation coil. An evident saturation of the magnetic field in the axial direction of the coil was observed and verified by experiments. Experimentally, the entire process, including the behavior of the magnetic field, was consistent with the numerical results. Based on the verified model, two main points were addressed: (1) Transient current distribution inside the coil during overcurrent charging was studied. Potential quenching risks were found to be at the innermost and outermost turn near the electrodes, as well as the pancake-to-pancake connection part. (2) Magnetic field saturation, which is a unique phenomenon in non-insulation superconducting coils during overcurrent charging, was studied in detail and first quantitatively defined by a new concept “converged load factor”. Its relationship with turn-to-turn resistivity was revealed.

Design and Optimization of Hybrid-Excited Claw-Pole Machine for Vehicle

In order to overcome the shortcomings of traditional electric excitation claw machine such as large leakage of magnetic field and easy saturation of ferromagnetic materials, a new topology structure with permanent magnet and electrical excited of shunt excitation scheme is proposed for claw-pole machine. Firstly, the output characteristics of voltage and current in power generation and electric state for claw-pole machine are analyzed by 3-D finite element method (FEM). And the influence of different excitation currents on the saturation state of magnetic circuit is calculated. On this basis, the influence of saturation of magnetic circuit is considered for electromagnetic torque and torque ripple. Therefore, under the condition of unsaturated flux density, in order to ensure the fastest and most stable start of the vehicle, it is necessary to obtain the maximum excitation current. Finally, a hybrid-excited claw-pole machine with rated power of 1.5kW is manufactured, and the on-load and no-load characteristics of prototype are tested to verify the feasibility of the hybrid-excited topology proposed.

Distributed variable stiffness joint assist mechanism based on laminated structure

Exoskeleton technology is more and more widely used in military, human rehabilitation, and other fields, but exoskeleton assisting mechanisms have problems such as high quality, concentrated driving sources, and poor flexibility. This article proposes a distributed variable stiffness joint power-assisted mechanism based on a laminated structure, which uses a giant magnetostrictive material as the driving source and the variable stiffness source of the structure. The distributed driving is realized by multiple driving units connected in series and parallel. Firstly, the drive unit stiffness matrix is deduced, and the expression equations of the cascaded total stiffness matrix of the drive module are obtained. After the simulation study, the curve of the stiffness of a single drive unit with a magnetic field and the stiffness of multiple drive units connected in series and parallel are in the absence of the magnetic field. The change curve of the stiffness of the booster module with the number of drive units under the excitation and saturation magnetic field excitation conditions is to achieve the effect of dynamically controlling the structural stiffness of the drive unit by controlling the size of the magnetic field and to obtain a general formula through data fitting. The number of drive units required under a fixed magnetic field excitation can ensure that the error is within 5%. The research results lay the foundation for further analysis of the distributed variable stiffness joint assist technology.

Strained CoFe2O4-amorphous SiO2 nanocomposites: Evaluation of structural and magnetic properties

Strained CoFe2O4 nanoparticles were dispersed in a SiO2 matrix prepared by the co-precipitation method. Rietveld refinement is performed to estimate structural parameters and distribution of cations at tetrahedral and octahedral sites respectively. W-H-ISM and W-H-ASM models were applied to evaluate lattice strain, crystallite size and lattice deformation stress. The decrease in coercivity and saturation magnetization observed with increased temperature and SiO2 content. Reduction in magnetization is attributed to the increased number of disordered surface spins with enhanced strain and reduced effective and surface anisotropy. The blocking temperature (TB)is evaluated as 347.9 K for CF, 349.2 K for 5%SiCF, 352.1 K for 10%SiCF and 353.4 K for 15%SiCF nanoparticles respectively. The Higher value of μSP(μB) is observed for CF nanoparticles at 350 K, represented in temperature and magnetic field dependent superparamagnetic moment (μSP(μB)) curves. A new dependency observed between variations of μSP(μB) with strain values as enhanced μSP(μB)is observed with increasing strain values for the higher concentration of SiO2. An enhancement in the saturation magnetic field (HHT) with increasing temperature confirms the necessity of a higher magnetic field for reaching saturation values. A new relation is examined for variation of Ms and μSP(μB) with strain values from 5 K to 350 K.

SN 2008iy circumstellar interaction: bright and lesser light effects

ABSTRACT Optical photometry and spectra of the luminous type IIn supernova SN 2008iy are analysed in detail with implications for cosmic ray acceleration and the radio emission. The light curve and expansion velocities indicate ejecta with the kinetic energy of 3 × 1051 erg to collide with the ∼10 M⊙ circumstellar envelope. The luminous H α is explained as originated primarily from circumstellar clouds interacting with the forward shock. For the first time the fluorescent O i 8446 Å emission is used to demonstrate that the cloud fragmentation cascade spans a scale range >2.3 dex. The narrow circumstellar H α permitted us to estimate the acceleration efficiency of cosmic rays. The found value is close to the efficiency inferred in the same way for other two SNe IIn, SN 1997eg and SN 2002ic. The efficiency of cosmic ray acceleration is utilized to reproduce the radio flux from SN 2008iy for the amplified magnetic field consistent with the saturated turbulent magnetic field in the diffusive shock acceleration mechanism.

Structural features and temperature-dependent magnetic response of cobalt ferrite nanoparticle substituted with rare earth sm3+

A series of samarium doped cobalt ferrites with the nominal compositions of CoSmxFe2−xO4 (where x = 0, 0.02, 0.04, and 0.06 at.%) was synthesized using sol–gel auto-combustion method. The crystal structure, morphology and magnetic properties of the nanoparticles have been investigated. The XRD data analyzed by the MAUD program confirmed the successful substitution of Fe3+ by Sm3+cations in the unit cell of the cobalt ferrite lattice. The formation of nanosized spinel ferrites was confirmed by FESEM and FTIR analysis. The values of saturation magnetization (MS) decreased from 76 emu/g to 63 emu/g by increasing the Sm content from x = 0 to x = 0.06 at room temperature, whereas at 10 K, the decreasing tendency of MS was much weaker. The reduction of temperature from 300 to 10 K caused a remarkable growth of both the saturation magnetization and coercive field (HC). The coercivity of the sample with x = 0.06 at 10 K is strongly higher than the one at the room temperature. The influence of samarium ions and temperature-dependent magnetic response of CoFe2O4 nanoparticles was studied and their effect was discussed in terms of the geometrical proportions and magnetic anisotropy evolutions. The Sm doped cobalt ferrite is a suitable candidate for moderate permanent magnets and high density information storage, especially when in use at low temperatures.

Peculiarity of the low temperature magnetoresistive effect in the Corbino disk with magnetic ordering

The transverse magnetoresistance (MR) hysteresis loops of a magnetically ordered Corbino disk have been studied in the temperature range 300–2 K in an external magnetic field with induction up to 1 T oriented in the plane of the disk (ϕ = 0°) and perpendicularly to its plane (ϕ = 90°). The Corbino disk is made of a thin permalloy film obtained on an insulating sitall substrate by ion-beam sputtering. Independently of the temperature and measurement geometry, the field dependences of MR in the range of weak magnetic fields up to the magnetisation saturation exhibit sharp peaks of the negative MR caused by the domain walls motion during the magnetisation reversal of the sample. The position of the peak in the magnetic field (Bp) is determined by the temperature as well as the angle between magnetic field direction and the disk plane. It was found that a temperature change in the range of T = 300–2 K leads to a change in its position in the range of 0.2–6.0 mT and 8–22 mT at ϕ = 0° and ϕ = 90°, respectively. The magnetic field direction reorientation from in-plane to out-of-pane at T = 2 K leads to the Bp change from 6 to 22 mT. In the range of strong magnetic fields above the magnetization saturation field at ϕ = 0° the positive MR component decreases with induction and has a linear non-saturable dependence down to T ≈ 40–50 K due to the magnon MR component dominance. The complete freezing of magnons at T = 2 K leads to the absence of high-field magnetoresistive effect. At ϕ = 90° in weak fields, the MR changes its sign from positive to negative due to the anisotropic MR component dominance because of the disk magnetisation reorientation perpendicular to the current lines. In a strong field it changes the slope due to the saturation of negative anisotropic MR component, as well as possible additional contribution of the positive geometric Lorentzian MR.

A comparison between structural and magnetic behavior of cobalt ferrite synthesized via solid state and chemical methods

Cobalt ferrite oxide (CoFe2O4) was synthesized by two different methods of mechanochemical and combustion. The phase composition and the chemical bonding information of the two powders were investigated by x-ray diffraction (XRD) method and Fourier Transform Infrared Spectroscopy (FT-IR). Field emission scanning electron microscopy (FESEM) was used to study the microstructure and morphology and elemental analysis was performed with EDS. The magnetic properties were analyzed at room temperature using a vibrating sample magnetometer (VSM). According to the structural and elemental analyses, cobalt ferrite was directly synthesized in the combustion method. However, the mechanochemical route was not successful in phase formation, even after heating at high temperatures. The hysteresis loops of VSM analysis showed that the CoFe2O4 powder from combustion method resulted in higher saturation magnetization and coercive field than the powder synthesized by mechanical milling. The inferior magnetic behavior of the powder from solid state method is attributed to the presence of Co3+ in the starting powder, which results in a non-spinel complex between cobalt and iron ions.

Study of martensitic transition temperature on Ni54Fe19Ga23X4 Heusler glass-coated microwires doped by X = B, Al, Ga, in

The influence of alloying in Ni54Fe19Ga23X4 Heusler glass-coated microwires doped by X = B, Al, Ga, In is presented in this work. Even though the alloys exhibit different chemical compositions, the valence electron concentration (e/a) was constant. Furthermore, basic magnetic and resistivity measurements have been performed to determine the chemical doping effect on the magnetic properties and the associated structural transformation. Results point to the fact that the fine-tuning of the chemical composition may be a suitable tool for adjusting the Curie temperature, transformation temperature, and magnetocaloric properties of the glass-coated microwires. In the case of Ga and the Al-doped alloy, a thermal hysteresis can be distinguished in the M(T) dependences at saturation magnetic field, pointing to the presence of the structural transformation. Moreover, the 4% Al doping shifts the structural transformation temperature and the Curie temperature almost to the same position. On the other hand, B and In doping may lead to the disappearance or shift of the structural transformation out of the measurement range (100–400 K). Resistivity measurements proved these results.

Large-scale magnetic field saturation and the Elsasser number in rotating spherical dynamo models

ABSTRACT Numerical simulations are used to investigate large-scale (mean) magnetic field generation in rotating spherical dynamos. Beyond a certain threshold, we find that the magnitude of the mean magnetic field becomes nearly independent of the system rotation rate and buoyancy forcing. The analysis suggests that this saturation arises from the Malkus-Proctor mechanism in which a Coriolis-Lorentz force balance is achieved in the zonal component of the mean momentum equation. When based on the large-scale magnetic field, the Elsasser number is near unity in the saturated regime. The results show that the large and small magnetic field saturate via distinct mechanisms in rapidly rotating dynamos, and that only the axisymmetric component of the magnetic field appears to follow an Elsasser number scaling.

Systematic investigation of the effect of layer thickness on the linear sensing characteristics of asymmetric structured CoFe/Rh/CoFe/Cu/CoFe fully epitaxial CIP-GMR based magnetic sensors

Giant magnetoresistance (GMR) devices known for their widespread application as magnetic field sensors face challenges owing to their nonlinear resistance response with the magnetic field. Here, we have developed CoFe(3 nm)/Rh(tRh nm)/CoFe(tmidCoFe nm)/bcc Cu(1.6 nm)/CoFe(ttopCoFe nm)/MgO(2 nm) based current in plane (CIP)-GMR devices and demonstrated linear MR curves with tunable characteristics. The MR ratio and saturating magnetic field were tunable between 3.9% and 23.5%, and 0.013 T and 1.5 T. The numerical simulation modeling confirmed biquadratic coupling between the bottom and middle CoFe layers through Rh and antiferromagnetic coupling between the middle and top CoFe layers through a Cu spacer, providing the linear MR. The fine-tuning of thicknesses of the middle and top CoFe layers provides supplementary routes for optimizing the sensitivity and operation field range of the CIP-GMR devices to specific magnetic sensor applications in the low and medium magnetic field range. The above results demonstrate that CIP-GMR devices with the asymmetric structure demonstrated in this study are promising for the next generation linear magnetic sensors.

Effect of oriented magnetic field on the solidified structure and soft magnetic properties of Fe78Si13B9 alloy

In this paper, the growth of dendrites and its effect on soft magnetic properties of Fe78Si13B9 alloy during solidification under the effect of 0.18 T oriented magnetic field are studied. It shows that the magnetic field has strong guiding and promoting effect on the growth of dendrites. The primary branches of the α-Fe (Si) phase dendrites grow in parallel along the vertical direction of the magnetic field line, and the length of the primary branches reaches more than 1 mm. At the same time, the secondary branches of the α-Fe (Si) phase dendrites also follow the direction of the magnetic field line. It grows directional parallel to the direction of the magnetic field line, and connects the adjacent primary branches to form a grid-like magnetically guided solidification structure with uniform spacing; The soft magnetic properties of the magnetically guided solidified(MGSed) FeSiB alloy are much better than the non-magnetically guided solidified(NGSed) FeSiB alloy, and the maximum permeability (μm) of MGSed FeSiB alloy is as high as 964.4789, which is twice as much as that of NGSed alloys. MGSed alloys have better resistance to magnetic field saturation, and their saturated magnetic field Hj value reaches 12,000 Oe, which is more than 3 times that of NGSed alloys. This work provides a novel route for further development of FeSiB alloys with excellent soft magnetism.

Modeling and Adaptive Control of Novel Electromechanical Inverter

A novel idea of electromechanical inverter (EMI) is proposed. This inverter minimize the complexity and cost of conventional rotating magnetic field inverters. The electromechanical inverter works on phenomena of rotating magnetic field in which changing flux in the external coils through dc motor induced an emf in the output coil. For controlling the speed of dc motor and rotation of coils, the adaptive control is used to avoid the saturation in magnetic field. The adaptive control system that is used for the electromechanical inverter (EMI) is model-reference adaptive control (MRAC) which has four parts i.e plant, reference model, adaptation mechanism and control law. An adaptation mechanism is designed with MIT rule of MRAC. The authenticity of proposed control technique for electromechanical inverter is verified by simulation results. The simulation result shows efficacy of proposed adaptive control technique using MATLAB

Low temperature rapid sol–gel auto-combustion synthesis and structural, morphological and magnetic study of nickel substituted cobalt nano ferrites

ABSTRACT The nickel substituted cobalt ferrite nanoparticles were synthesized via the sol–gel auto-combustion method. The single cubic spinel structure formation was confirmed from X-ray diffraction and Fourier transforms infrared spectroscopy study. The effect of lattice strain on crystalline size was studied using Williamson–Hall and the size-strain plot method. A microstructural study was performed using high-resolution field emission scanning electron microscopy. The magnetic properties were studied at room temperature using a vibrating sample magnetometer. The saturation magnetization obtained for pure cobalt nano ferrite was 79.66 emu/g comparable with the value for the bulk sample. The anisotropic constant and anisotropy field were found to be erg/cm3 and 88.66 kOe respectively for pure cobalt ferrite. The high value of saturation magnetization, anisotropic constant and anisotropy field of cobalt ferrite are important parameters for the application of prepared samples in data recording devices.

Preparation and structural investigation of Polyethylene glycol (PEG) / nano-ferrite composites

Polyethylene glycol (PEG)/nano-ferrite composites have been prepared by using CoFe2O4, CuFe2O4, Co0.5Cu0.5Fe2O4 and MgFe2O4 ferrite nano-particles synthesized by citrate precursor method along with PEG with different percentages. Ferrite samples have been characterized by X-ray diffraction (XRD) to confirm the formation of pure spinel ferrite phase and, transmission electron microscopy (TEM) to ensure that the average particle size is within the nano-scale. Thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) thermographs of the ferrite samples have been used to ensure the complete formation of pure ferrites at temperatures above 800oC. The ferrites and their composites with PEG, have been investigated by FTIR spectroscopy. The main bands of ferrites and PEG have been clearly displayed in agreement with literature. A systematic shift of the bands has been observed upon adding PEG. The magnetic properties have been explored by using the vibrating sample magnetometer (VSM). Where the values of of saturation magnetization (Ms), remnant magnetization (Mr) and coercive field (Hc) for pure ferrite and composite samples vary with the presence of different divalent cations which have different magnetic moment. Whereas, Hc values remain constant as obtained in pure ferrites regardless the ratio of PEG. The obtained values of Hc are comparable with those in literature, which can be used in electromagnetic wave attenuation.

Polar Kerr effect and perpendicular magnetic anisotropy in Fabry–Pérot cavity containing CoPt/AZO magneto-optical interference layer

We investigate the magneto-optical (MO) polar Kerr enhancement of Fabry–Pérot cavities with perpendicular magnetic anisotropy for chemical and biological sensing applications. The MO cavities consist of stacked films with a half-mirrored surface layer, a dielectric interference layer, a total-reflection mirror, and a magnetic metal layer. Co80Pt20 and Al-doped ZnO (AZO) thin films were utilized as the magnetic and interference layers, respectively. The cavities produce two types of MO enhancement depending on the thickness of the magnetic layer. The sample with a thick magnetic layer as a total-reflection mirror generates a single peak in the polar Kerr spectrum. Contrarily, inserting a several-nanometer-thick CoPt layer into the AZO layer produces a resonant-type spectrum. Although both samples generate large MO enhancement factors (>50), the magnetic properties significantly differ. The AZO/CoPt/AZO interference layer controls the crystalline and interface conditions and produces a square-shaped out-of-plane hysteresis loop with a large Kerr rotation angle. Moreover, the use of an ultrathin CoPt film significantly reduces the saturation magnetization field. Thus, Fabry–Pérot cavities with a CoPt/AZO interference layer may serve as high-sensitivity, low-energy-consumption sensor elements.