Behavior Of Magnetic Materials Research Articles

Comprehensive Magnetic Study of Nanostructured Mesoporous Manganese Oxide Materials and Implications for Catalytic Behavior

Magnetic behavior of nanostructured mesoporous manganese oxide materials, designated UCT-1 and UCT-18, were studied using a combination of superconducting quantum interference device (SQUID) magnetometry and 55Mn zero-field spin–echo nuclear magnetic resonance (NMR). Curie–Weiss fits to the magnetic susceptibility for the UCT-1 and UCT-18 samples calcined at 550 °C yielded paramagnetic moment values consistent with spin-only Mn3+ ions in the α-Mn2O3 phase (S = 2, 4.90 μB). However, the magnetization and NMR results reported here clearly identify a small amount of the Mn3O4 second phase (ferrimagnetic with TC ≈ 43 K) that does not appear in X-ray diffraction (XRD). The study resulted in the observation of fascinating magnetic behavior: (1) exchange bias, which occurs in cases where a ferromagnetic (or ferrimagnetic) phase forms a boundary with an antiferromagnetic phase and (2) a magnetic contribution attributed to uncompensated spins on the surfaces of the α-Mn2O3 nanoparticles. The presence of Mn3O4 and ...

Importance of matrix inelastic deformations in the initial response of magnetic elastomers.

Being able to predict and understand the behaviour of soft magnetic materials paves the way to their technological applications. In this study we analyse the magnetic response of soft magnetic elastomers (SMEs) with magnetically hard particles. We present experimental evidence of a difference between the first and next magnetisation loops exhibited by these SMEs, which depends non-monotonically on the interplay between the rigidity of the polymer matrix, its mechanical coupling with the particles, and the magnetic interactions in the system. In order to explain the microstructural mechanism behind this behaviour, we used a minimal computer simulation model whose results evidence the importance of irreversible matrix deformations due to both translations and rotations of the particles. To confirm the simulation findings, computed tomography (CT) was used. We conclude that the initial exposure to the field triggers the inelastic matrix relaxation in the SMEs, as particles attempt to reorient. However, once the necessary degree of freedom is achieved, both the rotations and the magnetisation behaviour become stationary. We expect this scenario not only to be limited to the materials studied here, but also to apply to a broader class of hybrid SMEs.

How to include frequency dependent complex permeability Into SPICE models to improve EMI filters design?

Electromagnetic interference (EMI) filters design is a rather difficult task where engineers have to choose adequate magnetic materials, design the magnetic circuit and choose the size and number of turns. The final design must achieve the attenuation requirements (constraints) and has to be as compact as possible (goal). Alternating current (AC) analysis is a powerful tool to predict global impedance or attenuation of any filter. However, AC analysis are generally performed without taking into account the frequency-dependent complex permeability behaviour of soft magnetic materials. That’s why, we developed two frequency-dependent complex permeability models able to be included into SPICE models. After an identification process, the performances of each model are compared to measurements made on a realistic EMI filter prototype in common mode (CM) and differential mode (DM) to see the benefit of the approach. Simulation results are in good agreement with the measured ones especially in the middle frequency range.

Synthesis and structural, magnetic characterization of nanocrystalline Zn1-xCoxO diluted magnetic semiconductors (DMS) synthesized by combustion reaction

Nanocrystalline Co+2 doped Zn1−xCoxO, where x = 0.02, 0.03, 0.07 and 0.1mol of Co+2 diluted magnetic semiconductors (DMS), were synthesized by combustion reaction for spintronic applications. The effects of Co+2 ion doping on the structural, morphological and magnetic properties of ZnO ware investigated. The products of the reactions were characterized by X-ray diffraction (XRD), nitrogen adsorption (BET), transmission electron microscopy (TEM), and magnetic measurements (VSM). XRD spectra data revealed the formation of a ZnO phase (removed text), indicating that the synthesis was efficient in diluting the Co+2 ions in the ZnO lattice. Increasing the Co2+ ion concentrations reduced the maximum reaction and ignition temperature and contributed to reduce crystallite and particle sizes. The samples showed the typical behavior of soft magnetic materials at all the Co2+ concentrations evaluated here. The Curie temperature (Tc) was higher than room temperature at all the Co2+ concentrations.

Quantitative Design of a High Performance Permanent Magnet Vernier Generator

Permanent-magnet vernier machines are becoming more and more attractive due to their high torque density and low-speed operating capabilities. This paper investigates the effects of the magnet thickness, magnet pole arc ratio, and slot open ratio on the torque capacity. An analytical model is first presented. It is validated by comparing the results with the finite-element analysis (FEA) under the same hypothesis. A mono-objective optimization is then conducted on the basis of the analytical model coupled to genetic algorithm to reach the optimal values yielding the highest value of the torque. Finally, the influence of nonlinear magnetic material behavior on the optimal design is investigated through nonlinear FEA. The results are presented and discussed.

Synthesis and Characterization of B2O3Additive on Ni-Cu-Zn ferrites by Solid State Reaction Method

Ni-Cu-Zn ferrites are well-known technological magnetic materials used for manufacturing of multilayer chip inductor and applications in various electrical devices. The work is focused on the persuade of substitutions and sintering additive B2O3 on structural, transport and electromagnetic properties of Ni-Cu-Zn ferrites. The composition Ni0.28Cu0.10Zn0.62Fe2O4 + x wt. % where x= 0.2 to 0.8 for V2O5 was prepared by using the solid state reaction technique sintered at 1200oC with 6 hours holding time. Lattice parameters of Ni0.28Cu0.10Zn0.62Fe2O4 + x wt. % Bi2O3 are slightly decrease with increase x content. The grain growth by increasing the additives Bi2O3 content inter diffusion as results after > 0.4wt. % Bi2O3 content abnormal grain growth. Curie temperature (Tc) decreases continuously with increase of doped Bi2O3 additives in ferrite samples. The magnetization process all the samples are soft magnetic behavior of magnetic materials. Initial permeability (µi) decreases with increasing doped Bi2O3 content in ferrite samples and hence the highest value of quality factor is found for x = 0.4 within the range 20 kHz to 2MHz. The µi shows the flat profile from 1 kHz to 4MHz indicating frequency stability for all the ferrite samples. The visible grain growth indicates the improved electromagnetic properties. DC resistivity decreases with increasing temperature shows the semiconducting nature of the sample. With increasing the frequency, the dielectric constant is found to decrease continuously and remain almost frequency independent at higher frequency range.

Synthesis and Characterization of B2O3Additive on Ni-Cu-Zn ferrites by Solid State Reaction Method

Ni-Cu-Zn ferrites are well-known technological magnetic materials used for manufacturing of multilayer chip inductor and applications in various electrical devices. The work is focused on the persuade of substitutions and sintering additive B2O3 on structural, transport and electromagnetic properties of Ni-Cu-Zn ferrites. The composition Ni0.28Cu0.10Zn0.62Fe2O4 + x wt. % where x= 0.2 to 0.8 for V2O5 was prepared by using the solid state reaction technique sintered at 1200oC with 6 hours holding time. Lattice parameters of Ni0.28Cu0.10Zn0.62Fe2O4 + x wt. % Bi2O3 are slightly decrease with increase x content. The grain growth by increasing the additives Bi2O3 content inter diffusion as results after > 0.4wt. % Bi2O3 content abnormal grain growth. Curie temperature (Tc) decreases continuously with increase of doped Bi2O3 additives in ferrite samples. The magnetization process all the samples are soft magnetic behavior of magnetic materials. Initial permeability (µi) decreases with increasing doped Bi2O3 content in ferrite samples and hence the highest value of quality factor is found for x = 0.4 within the range 20 kHz to 2MHz. The µi shows the flat profile from 1 kHz to 4MHz indicating frequency stability for all the ferrite samples. The visible grain growth indicates the improved electromagnetic properties. DC resistivity decreases with increasing temperature shows the semiconducting nature of the sample. With increasing the frequency, the dielectric constant is found to decrease continuously and remain almost frequency independent at higher frequency range.

Study of critical behavior using the field dependence of magnetic entropy change in La0.7Sr0.3Mn1-xCuxO3 (x = 0.02 and 0.04)

We report the magnetic properties and critical behavior of La0.7Sr0.3Mn1-xCuxO3 (x = 0.02 and 0.04) perovskite manganites. Results of temperature-dependent magnetization show that the Curie temperature decreases from 360K (x = 0.02) to 356K (x = 0.03) with increasing Cu content. Field dependence of isothermal entropy change data is used to estimate the critical exponents, and the results satisfied the requirements of the scaling law. Calculated critical exponents are β = 0.4641, γ = 1.1623, and δ = 3.546 for x = 0.02, and β = 0.4486, γ = 1.2024, and δ = 3.6805 for x = 0.04. These results indicate that La0.7Sr0.3Mn1-xCuxO3 can be characterized by long-range mean-field behavior. Thus, the field dependence of magnetic entropy change can be effectively used in studying the critical behavior of magnetic materials.

Dynamic Modeling and Simulation of Short-Duration Over-excitation Phenomenon in Hysteresis Motor

The hysteresis motor is a well-known synchronous motor that is used in special small power, high speed applications. Dynamic modeling and analysis of this motor is more complicated than permanent magnet synchronous motors (PMSMs) or induction motors (IMs) due to nonlinear behavior of rotor magnetic material. Short over-excitation is a unique phenomenon that only occurs in hysteresis motor in which the terminal voltage increase at synchronous speed for a short duration, and then continuously is decrease to initial value. Therefore, the input current is reduced, this leads to more power factor and efficiency enhancement. Till now, there isn’t any analytic dynamic model of this phenomenon. In this paper, based on a novel dynamic model of hysteresis motor, the over-excitation phenomenon is investigated and transient performance of the motor during over-excitation is simulated via Simulink.

Tunable magnetism of 3d transition metal doped BiFeO3

Electronic polarization or bond relaxation can effectively alter the electronic and magnetic behavior of materials by doping impurity atom. For this aim, the thermodynamic, electronic and magnetic performances of cubic BiFeO3 have been modulated by the 3d transition metal (TM) dopants (Sc, Ti, V, Cr, Mn, Co, Ni, Cu and Zn) based on the density functional theory. Results show that the doped specimen with low impurity concentration is more stable than that with high impurity concentration. The Mulliken charge values and spin magnetic moments of TM element are making major changes, while those of all host atoms are making any major changes. Especially, it is the linear relation between the spin magnetic moments of TM dopants and the total magnetic moment of doped specimens; thus, the variations of total magnetic moment of doped specimens are decided by the spin magnetic moments of TM dopants, thought the total magnetic moments of doped specimens mainly come from Fe atom and TM dopants. Besides, as double TM atoms substitution the Fe atoms, the Sc-, Ti-, Mn-, Co- and Zn-doped specimens show AFM state, while the V-, Cr-, Ni- and Cu-doped specimens show FM state.

Influência do teor de Zn2+ nas características morfológicas e magnéticas de ferritas Mn1-xZnxFe2O4 sintetizados em grande escala por reação de combustão

Resumo Este trabalho teve como objetivo avaliar a influência do Zn2+ nas características morfológicas e magnéticas de ferritas Mn1-xZnxFe2O4 (onde x= 0,0, 0,35, 0,5 e 0,65 em mol de Zn) sintetizadas por reação de combustão em escala piloto com bateladas de 200 g/reação. As amostras foram caracterizadas por difração de raios X, microscopia eletrônica de varredura/transmissão e medidas magnéticas. Os resultados indicaram que todas as composições de ferritas foram monofásicas; morfologicamente a adição de Zn ao sistema MnFe2O4 causou leve redução no tamanho dos aglomerados e redução no tamanho das partículas, mas esse comportamento não foi linear com o teor de Zn2+. As amostras apresentaram comportamento magnético característico de materiais magnéticos moles, com magnetização de saturação máxima de 62 emu/g para a amostra com menor teor de zinco em sua composição.

Studies on Chemical and Physical Properties of LiFeMPO<sub>4</sub> (M=Cu, La) by Polyol Route

Bare Lithium Iron Phosphate (LiFePO4), Cu, La doped and Cu with La co-doped LiFePO4 composite materials have been prepared via polyol technique without further post heat treatment. The prepared bare and composite materials’ crystalline structure has been indexed an orthorhombic phase olivine structure with space group of Pnma. The functional group vibrations and surface morphology of the prepared materials has been observed using Fourier transfer infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) with EDX analyses. Magnetization measurements revealed that saturation magnetizations (Ms) of the metal doped samples are gradually increased than that of the pure LiFePO4. All the samples exhibit the spin-glass behaviour of magnetic materials.

Temperature evolution of broadband magnetization behavior in dual-phase soft magnetic compacted materials

This study examines the effect of operating temperature (from 23°C to 110°C) on broadband (from 1Hz to 1MHz) fluxmetrically obtained complex permeability spectra and energy loss in a set of dual-phase compacted soft magnets composed of pulverized alloys Co56Fe16Zr8B20 and Fe72.5Cu1Nb2Mo2Si15.5B7 consolidated in supercooled liquid conditions for CoFeZrB alloy constituent. The investigated samples differ in mass ratio of these two constituents (from 10wt.% to 50wt.% of FeCuNbMoSiB). The complete loss separation into the components produced by domain walls and magnetization rotation is performed. It is found that domain walls in such type of materials are fully relaxed beyond several kHz. Further analysis suggests that the domain wall movement is easier in materials subjected to higher temperatures as a result of reversible removal of a part of anisotropy. Nevertheless, the rotation contribution is temperature independent. In cores with lower content (10wt.%) of FeCuNbMoSiB, temperature of 100°C causes an increase in low-frequency (100Hz) real permeability by 15%, while at higher amount (50wt.%) only by 4% with respect to room temperature.

Detection of magnetic circular dichroism with subnanometer convergent electron beams

The electron energy-loss spectroscopy technique known as electron magnetic circular dichroism (EMCD) has enormous potential for quantitatively probing the magnetic behavior of materials on the nanoscale. However, the requirement for mostly parallel illumination conditions greatly complicates the extraction of EMCD signals from surface areas under a few square nanometers, because scanning probe methods are limited to around this spatial resolution by the need for higher convergence angles. Here we propose theoretically and demonstrate experimentally that EMCD detection is feasible with convergence angles that are sufficiently large even for atomic resolution spectroscopy. Utilizing scanning transmission electron microscopy we experimentally detect a clear EMCD signal from a 50-nm-thick sample of bcc iron using a convergence semiangle of 8 mrad at 300 keV acceleration voltage, resulting in a probe size of approximately 2 \AA{}. We subsequently estimate the number of chirally scattered electrons needed for an unambiguous detection of the EMCD signal and present a method to quantify confidence in signal detection.

Magnetic anisotropy induced by crystallographic orientation and morphological alignment in directionally-solidified eutectic Mn-Sb alloy

The influences of the crystallographic orientation and morphological alignment upon the magnetic anisotropic behavior of polycrystalline materials were investigated. Microstructures obtained in eutectic Mn-Sb alloys via directional solidification simultaneously displayed crystallographic orientation and morphological alignment. Both the crystallographic orientation and the morphological alignment were able to induce magnetic anisotropy in the alloys, wherein the influence of the crystallographic orientation and the morphological alignment upon the magnetic anisotropic behavior of the alloys strongly depended upon their directions and exhibited either mutual promotion or competition. These findings may provide useful guidance for the fabrication design of functional magnetic materials.

Microstructure and rheology of magnetic hybrid materials

In this paper, an overview on a class of materials with high actual research interest will be given. Magnetic hybrid materials, i.e. liquid or elastic matrices filled with magnetic nano- or micro-particles provide the possibility to influence their mechanical behaviour by application of technically easily realizable magnetic fields. In particular, the viscous and elastic behaviour of magnetic hybrid materials can be influenced by magnetic fields. The physical reason for these changes are field-induced reconfigurations of the microstructure formed by the magnetic particles. Experimental techniques to observe these changes and their relation to changes in the mechanical behaviour of magnetic hybrid materials will be in focus of this review.

Synthesis of FeNi Alloy Nanomaterials by Proteic Sol-Gel Method: Crystallographic, Morphological, and Magnetic Properties

Proteic Sol-Gel method was used for the synthesis of FeNi alloy at different temperature conditions and flow reduction. The solids were characterized by XRD, H2-TPR, SEM, TEM, Mössbauer spectroscopy, and VSM. It was observed by X-ray diffraction pure FeNi alloy in the samples reduced at 600°C (40 mL/min H2 flow) and 700°C (25 mL/min H2 flow). The FeNi alloy presented stability against the oxidizing atmosphere up to 250°C. The morphology exhibited agglomerates relatively spherical and particles in the range of 10–40 nm. Mössbauer spectroscopy showed the presence of disordered ferromagnetic FeNi alloy, and magnetic hysteresis loop revealed a typical behavior of soft magnetic material.

Evaluation of the Processing Conditions in the Transesterification for Biodiesel Production Using the Nanomagnetic Catalyst Ni<sub>0.</sub><sub>5</sub>Zn<sub>0.</sub><sub>5</sub>Fe<sub>2</sub>O<sub>4</sub>

Magnetic catalysts are easily removed from the reaction process, thereby reducing the wastewater generation. Therefore, the study proposes to evaluate the performance of the nanomagnetic catalyst Ni0.5Zn0.5Fe2O4 in the transesterification reaction of the soybean oil to produce biodiesel, varying processing conditions (temperature, molar ratio of oil:alcohol and catalyst amount) on the catalytic reaction. The catalyst was synthesized by combustion reaction and characterized by XRD, BET, magnetic measurements and gas chromatography. The results revealed the inverse spinel phase formation, type B(AB)2O4, with isotherm profile classified as type V with hysteresis loop of type 3 (H3), and surface area of ​​48.39 m2g-1. The magnetic hysteresis curve showed a characteristic behavior of soft magnetic material with saturation magnetization value of 55 emu/g. Chromatographic analysis confirmed that the magnetic nanoparticles are catalytically active and that the processing conditions directly influence the conversion into esters.

OBTAINING HYSTERESIS LOOPS AT LOW FREQUENCY FOR CHARACTERIZATION OF MATERIALS TO BE USED IN BIOMEDICAL APPLICATIONS

The promising development of magnetic sensors in biomedical field demands an appropriate level of understanding of the magnetic properties of the materials used in their fabrication. To date only few of the types of magnetic materials are encountered where their magnetic properties, characterization techniques and magnetization behavior are yet to be explored more suitably in the light of their applications. This research work studies the characterization of materials by using a cost effective and simple circuit consisting of inductive transducer and an OP-AMP as a voltage integrator. In this approach the circuit was simulated using PSPICE and experiments have been conducted to achieve the desired results. The simulation and experimental results are obtained for three test materials namely iron, steel and plastic. The novelty lies in applying the simple circuit for material testing and characterization via obtaining simulation results and validating these results through experiment. The magnetic properties in low external magnetic field are studied with materials under test. The magnetization effect of a magneto-inductive sensor is detected in low frequency range for different magnetic core materials. The results have shown magnetization behaviour of magnetic materials due to the variation of permeability and magnetism. The resulted hysteresis loops appeared to have different shapes for different materials. The magnetic hysteresis loop found for iron core demonstrated a bigger coercive force and larger reversals of magnetism than these of steel core, thus obtaining its magnetic saturation at a larger magnetic field strength. The shape of the hysteresis loop itself is found to be varying upon the nature of the material in use. The resulted magnetization behaviors of the materials proved their possible applicability for use in sensing devices. The key concern of this work is found upon selecting the appropriate magnetic materials at the desired frequency of operation for magneto resistive applications, magneto-resistive sensors and for an extensive range of biomedical sensor application.Â

A Comparative Study: Dynamic and Thermal Behavior of Nanocrystalline and Powder Magnetic Materials in a Power Converter Application

In the design of such power electronics applications as power converters, lack of precise characterization and diagnosis of losses from components has unacceptable effects on efficiency, reliability, and power consumption. Because passive components, especially magnetic components, are crucially important in power converters, accurate characterization and modeling of magnetic materials is mandatory, to enable realistic prediction of their behavior under variable operating conditions. Temperature is one such condition that induces major changes in a component’s behavior by modifying the material’s magnetic properties. In the work discussed in this paper we investigated the magnetic and thermal behavior of nanocrystalline and powder materials in a DC–DC converter application. Core loss measurements under variable conditions were performed on toroid-shaped samples. Measured results were analyzed for different frequencies, flux densities, and temperatures.