Magnetostatic Measurements Research Articles

Synthesis of Co-Ni Alloy Particles with the Structure of a Solid Substitution Solution by Precipitation in a Supercritical Carbon Dioxide.

Mixed Co-Ni bimetallic systems with the structure of a solid substitution solution have been synthesized using the supercritical antisolvent precipitation (SAS) method, which uses supercritical CO2 as an antisolvent. The systems obtained have been characterized in detail using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared (FTIR) spectroscopy, and magnetostatic measurements. It has been found that Co-enriched systems have a defective hexagonal close-packed (hcp) structure, which was described by a model which embedded cubic fragments of packaging into a hexagonal close-packed (hcp) structure. It has been shown that an increase in water content at the precipitation stage leads to a decrease in the size of cubic fragments and a more uniform distribution of them in Co-enriched systems. It has also been shown that mixed systems have the greatest coercivity in the line of samples. Ni-enriched bimetallic systems have a cubic close-packed (ccp) structure with modified crystal lattice parameters.

An Indirect Method of Micromagnetic Structure Estimation in Microwires.

The tunable magnetic properties of amorphous ferromagnetic glass-coated microwires make them suitable for a wide range of applications. Accurate knowledge of the micromagnetic structure is highly desirable since it affects almost all magnetic properties. To select an appropriate wire-sample for a specific application, a deeper understanding of the magnetization reversal process is required, because it determines the measurable response (such as induced voltage waveform and its spectrum). However, the experimental observation of micromagnetic structure of micro-scale amorphous objects has strict size limitations. In this work we proposed a novel experimental technique for evaluating the microstructural characteristics of glass-coated microwires. The cross-sectional permeability distribution in the sample was obtained from impedance measurements at different frequencies. This distribution enables estimation of the prevailing anisotropy in the local region of the wire cross-section. The results obtained were compared with the findings of magnetostatic measurements and remanent state analysis. The advantages and limitations of the methods were discussed.

Modelling and identification of switched reluctance machine inductance

ABSTRACT Identification of phase self-inductance is a central step in control and development of Switched Reluctance Machine (SRM) model because the voltage and torque equation are functions of the phase self-inductance. The SRM operates primarily in the saturation region because the power factor is lower in the linear region, which makes the SRM modelling difficult to achieve. The strong nonlinearity of this machine must be taken into consideration by appropriate identification of the inductance parameters. This paper presents a new method for analytical modelling and identification of nonlinear inductance at standstill tests. We have shown that our electrical model of SRM can be described by Hammerstein model as a typical nonlinear model with a specific structure. The proposed method differs substantially from the existing used to identify the inductance of SRM. The results of this analytical approach are compared with those obtained using magnetostatic finite element method and experimental measurement. The comparison results show good accuracy of the identified model.

Синтез и магнитные свойства соединений Y0,5Ca0,5Cr0,5Mn0,5O3

In this work,a solid solution of chromite-manganite of the composition Y0,5Ca0,5Cr0,5Mn0,5O3 was synthesized using the sol-gel method. Based on the results of experimental studies of the magnetostatic properties of the polycrystalline system Y0,5Ca0,5Cr0,5Mn0,5O3. It is found that the predominant is the intracrystalline ferromagnetic interaction, while the intercrystalline interaction is antiferromagnetic in nature.In the field of 2000 Oe and 5000 Oe at a temperature of 5 K, the magnetic moment is not even positive. These dependencies were obtained after the sample was in a large negative field. This initial moment is approximately equal to the residual moment on the hysteresis loop for a temperature of 5 K. When the external field is increased gradually, for example, in increments of 250 Oe, this moment increases to 1.2 emu/g at 2000 Oe. Based on the results of magnetostatic measurements, it was found that hysteresis loops of magnetization are observed at low temperatures.

Variation of microwave magnetic properties for thin films of ferromagnetic metals with the film thickness

An investigation of the dependence of magnetic properties on the thickness of ferromagnetic films was completed. The study dealt with magnetostatic and microwave measurements of single-layer films of ferromagnetic metals (Fe, Co) and was aimed at revealing reasons for the deterioration of microwave magnetic performance with an increase in film thickness. Two types of variation of microwave permeability with the film thickness were distinguished for the films under study. One exhibited a noticeable deviation from maximal values and was observed for Co. The other case involved a gradual worsening of performance, and was observed for Fe. In the first case, the resonance frequency shifted lower when the film was thicker than 0.2–0.4 μm, and Acher’s coefficient fell by the factor of three. In the second case, the microwave performance worsened gradually, and a decrease of Acher’s coefficient was not large, approximately by 20%. The data analysis showed that the reason for the deterioration is an increase of out-of-plane anisotropy in the first case and sufficient growth of damping factor in the second case.

Noise characterization for the FID signal from proton precession magnetometer

Proton precession magnetometer is a high-precision device for weak magnetostatic field measurement. The measurement accuracy depends on the frequency measurement of free induction decay (FID) signal, while the signal to noise ratio (SNR) is an important factor affecting the results. Many signal processing methods have been proposed to improve the SNR of FID signal. However, the theoretical analysis of different types of noises for FID signal has not be conducted yet. In addition, the relationship between the frequency measurement accuracy and SNR has not been explicitly established and quantified. This paper first proposes a background noise model based on the extracted features from the FID signal. With this model, background noises, such as white noise, narrow-band noise, and phase noise etc., can be calculated and estimated. Secondly, the relationship between the frequency measurement accuracy and SNR is identified. We also built a prototype proton magnetometer for field tests and validation purpose. Experiments were conducted to investigate this relation through simulation. Different values for frequency accuracy were obtained with different SNRs from the acquired FID signals from field tests. The consistence between the measurement and computational results is observed. When SNR is larger than 30 dB, the absolute frequency accuracy becomes constant which is about 0.04 Hz. With the stability taken into account, the accuracy can be better even when the SNR is higher than 30 dB. This study provides a reference to optimize the design of proton precession magnetometer and the frequency calculation for FID signal.

Lanthanum-strontium manganites for magnetic nanohyperthermia: Fine tuning of parameters by substitutions in lanthanum sublattice

Ln-doped La0.7−xLnxSr0.3MnO3 (Ln – Nd and Sm) nanoparticles were synthesized via sol-gel method with further heat treatment at 800 °C. Crystallographic, magnetic and calorimetric properties of the obtained nanoparticles have been studied. According to X-ray data, all particles have crystalline perovskite structure and lattice cell volume decreases with growing Ln content. It follows from magnetostatic measurements that the increase in Ln content results in lowering Curie temperature and reduction of room-temperature magnetization. Calorimetric studies show that the action of an external alternating magnetic field causes the effective heating of nanoparticles at temperatures lower than Curie temperature, while heating efficiency strongly weakens upon a transition into paramagnetic state. Thus, fine tuning of the Curie temperature of nanoparticles allows controlling the maximal temperature achieved during the heating, which is important for application of these materials as mediators of self-controlled magnetic nanohyperthermia.

Peculiarities of magnetic properties of magnetoactive elastomers with hard magnetic filler in crossed magnetic fields

The purpose of this work was to research the influence of interparticle interactions, the elastic properties of matrix and the method of particles preparation on the magnetic properties of the magnetoactive elastomers based on polyurethane rubber containing magnetic particles with high coercivity both conducting and non-conducting. Magnetostatic properties measurements of magnetoactive elastomers were carried out using Vibrating Sample Magnetometer. The diagonal components of susceptibility tensor were found. The dynamic magnetic susceptibility (non-diagonal components) of magnetoactive elastomers was found with immitance-meter using a coil with an elastomeric core. The measured static and dynamic parameters of different samples were compared with each other. Mechanisms of magnetization changes in parallel and crossed magnetic fields are discussed.

An undergraduate laboratory experiment for measuring ε0, μ0 and speed of light c with do-it-yourself catastrophe machines: electrostatic and magnetostatic pendula

An experimental set-up for electrostatic measurement of , separate magnetostatic measurement of and determination of the speed of light according to Maxwell’s theory with percent accuracy is described. No forces are measured with the experimental set-up, therefore there is no need for a scale, and the experiment cost of less than £20 is mainly due to the batteries used. Multiplied 137 times, this experimental set-up was given at the Fourth Open International Experimental Physics Olympiad (EPO4) and a dozen high school students performed successful experiments. The experimental set-up actually contains two different pendula for electric and magnetic measurements. In the magnetic experiment the pendulum is constituted by a magnetic coil attracted to a fixed one. In the electrostatic pendulum when the distance between the plates becomes shorter than a critical value the suspended plate catastrophically sticks to the fixed one, while in the magnetic pendulum the same occurs when the current in the coils becomes greater than a certain critical value. The basic idea of the methodology is to use the loss of stability as a tool for the determination of fundamental constants.

Quasi-static magnetic properties and high-frequency energy losses in CoFe2O4nanoparticles

Two series of nanosized cobalt spinel ferrites CoFe2O4 are synthesized from metal salts using high-energy ball milling with the addition of NaCl as a growth agent (series CFO-NaCl), and without (CFO Series). The particle properties are characterized using atomic force microscopy, as well as magnetic and calorimetric measurements. It is shown that the average sizes of the nanoparticles were ∼5.6 and ∼10.3 nm for CFO and CFO-NaCl series, respectively. We performed magnetostatic measurements and determined the parameters that are required to analyze the magnetic state and remagnetization processes of the nanoparticles. It is shown that the blocking temperature is ≈160 K for CFO samples and ≈300 K for the CFO-NaCl series. It was concluded that at 293 K the CFO series particles exhibit a superparamagnetic state, whereas the CFO-NaCl series are in the blocked state. The specific loss power that is scattered by the synthesized nanoparticle ensembles placed in an alternating magnetic field, is measured experimentally and theoretically assessed. The nature of the processes that determine the thermal characteristics of the nanoparticles is analyzed.

Effect of Perpendicular Anisotropy and Eddy Currents on the Microwave Performance of Single-Layer and Multi-Layer Permalloy Films

In this letter, microwave and magnetostatic measurements of single- and multilayer Permalloy films are made to find physical reasons causing the decrease of the microwave permeability of the films with increase in film thickness. The permeability is measured in the frequency range of 0.1–10 GHz by a coaxial technique. From the measured permeability, a contribution to the effective field from the magnetoelastic effect is determined. The decrease of microwave permeability in thick films is shown to arise mainly due to the perpendicular magnetic anisotropy rather than from the effect of eddy currents, as is frequently suggested. It is also shown that both these effects are reduced in multilayer films comprising alternating magnetic and dielectric layers. Therefore, such films are promising materials for developing magnets that possess high permeability at high frequencies.

Theoretical Analysis of Experimental Valence and Magnetization Data around the Field- and Temperature-Induced Valence Transitions of EuNi2(Si0.18Ge0.82)2: Unified Interpretation for the Results from Soft X-ray Absorption, Its Magnetic Circular Dichroism, and Magnetostatic Measurements

We calculate the valence and the magnetization as functions of magnetic field and temperature for EuNi2 (Si0.18Ge0.82)2 with a single impurity Anderson model (SIAM), taking into account the effects of (i) the first-order nature of field- and temperature-induced valence transitions, (ii) magnetic impurities, and (iii) the Van Vleck paramagnetism for the Eu3+ state, as well as of the mixed valency between the Eu2+ and Eu3+ configurations. The results are in good agreement with recent experimental results by the soft X-ray absorption and X-ray magnetic circular dichroism experiments and also with available data of magnetization measurements. The present SIAM is an improved version of that used to analyze the field-dependent valence observed by hard X-ray absorption measurements. We point out a serious inconsistency between experimental data for the valence observed by hard X-ray experiments and the magnetization curve, but this inconsistency is removed by the new valence data observed by soft X-ray experiments.

The Internal Pressure Test in Experiment and Simulation—Influence of the Wall Thickness Variation and the Change of the Packaging Behavior after the Impact of Standard Liquids

The effect of the wall thickness variation of blow‐moulded bodies made of high‐density polyethylene on an internal pressure test after prestoring the packaging with standard liquids was evaluated in experiments and simulations. The objects of the investigation were jerrycans used for the transportation and storage of dangerous goods.The wall thickness was determined using two alternative methods to the magnetostatic measurement. These alternative methods are used for research purpose to get a volumetric model of the jerrycan wall as a geometric model for the simulation. The comparison of the experiments and the simulations of the internal pressure test were performed using the digital image correlation method. The integral strain and deformation of the whole jerrycan was detected by measuring the total mass of the jerrycan being filled with water during the internal pressure test. This is a suitable alternative to the optical measurements of local deformation by the digital image correlation method. Prestorage at 40 °C without the influence of chemicals strengthens the jerrycan, whereas the swelling effect of butyl acetate and hydrocarbon mixture softens the jerrycan. The comparison with the experiment is necessary to verify the accuracy of the simulation. It shows that the deformation can be simulated more precisely by using the actual measured geometry. The weakening of the high‐density polyethylene caused by a hydrocarbon mixture can be simulated using the Arrhenius equation. The aim of the simulation was to discover whether it is possible to use specimens to predict the behaviour of a packaging both after the influence of standard liquids. Copyright © 2012 John Wiley & Sons, Ltd.

Growth-induced perpendicular anisotropy of grains in Co-Al-O nanogranular ferromagnetic films

This paper reports on the results of the magnetostatic measurements for Co-Al-O nanogranular films over a wide range of concentrations of the ferromagnetic component x. It has been revealed that grains in the films are characterized by the growth-induced anisotropy with easy axes directed perpendicular to the film plane. The maximum field of the single-grain perpendicular anisotropy reaches ∼2.5 kOe for samples in the vicinity of the percolation threshold (x ≈ 61 at % Co). It has been established that the characteristic features of the superparamagnetic behavior of an ensemble of oriented Stoner-Wohlfarth particles are retained for the sample with x ≈ 61 at % Co in the presence of the demagnetization field associated with the net magnetization of the film. The influence of the demagnetization field of the film on the shape of the magnetization reversal curves, the coercivity, and the blocking temperature has been investigated and simulated. The results of the simulation are consistent with the experimental data.

Method for Evaluating Shielding Factor of Magnetically Shielded Room for Uniform Magnetic Field Using Exciting Coil

To shield environmental magnetic noise, magnetically shielded rooms (MSRs) made of ferromagnetic materials are used for biomagnetic measurements. The shielding performances of MSRs are usually represented by the shielding factor, SF. The source of environmental noise is far away from the MSR, so that almost uniform magnetic field is applied to the MSR. Therefore, the shielding factor SF0 for uniform magnetic field needs to be evaluated. To evaluate SF at a construction site, magnetic noise is applied to the MSR by coils. However, the magnetic noise generated by coils is not uniform, and SFs depend on the sizes and positions of the coils and are not unique for the same MSR. Therefore, standardization of a method to evaluate SF0 accurately using coils is being discussed by the Japan Electronics and Information Technology Industries Association (JEITA). We discuss here a method for estimating the SF0s of MSRs by placing a smaller coil near the MSR under the condition with very low frequency, in which the eddy current effect can be neglected, using both 3D linear and nonlinear magnetostatic field analyses and measurements. A method to estimate SF0s by extrapolation using simple numerical expressions representing the relation between the SF and the size and the position of the coil is proposed in the 3D linear magnetostatic analysis. The proposed method is applied to an experiment with a single-layered MSR under ideal conditions. Namely, MSR is placed in a spacious building so that the experiment is not affected by the steel frames and the reinforcing bars of the building. Moreover, the door of MSR does not affect its SFs. In these conditions, we were able to accurately estimate SF0s in the experiment.

Comparative performance of static-mode ferrous MEMS gradiometers fabricated by a three-step DRIE process

Two MEMS structures—a cantilever beam and a quad-beam—have been designed and fabricated through a three-step deep reactive ion etching (DRIE) process. Devices feature target patterns to align with an external optical detection system and a micromachined cavity to embed an NdFeB hard mini-magnet, thus releasing the stress of structures. Structures are intended for magnetostatic gradient measurements. Induced magnetic fields generate an attracting force on the magnet that deflects the sensor. Deflection is optically detected through nanometer-resolution confocal microscopy. The static-mode sensitivity of up to 1.86 × 10−4 T m−1 demonstrates that MEMS gradiometers are able to perform in situ gradiometry with a single sensor and miniaturized size. Suitable techniques for integrated detection are discussed.

Magnetic and dielectric properties in the langasite-type compounds:A3BFe3D2O14(A=Ba, Sr, Ca; B=Ta, Nb, Sb; D=Ge, Si)

The Fe-based langasites are the first reported compounds presenting a magnetic ordering in this rich family, besides being well known for piezo-electric properties and optical activity. The structural, magnetic and dielectric properties of the Fe langasite compounds, with various substitution of non-magnetic cations, have been studied with x-ray and neutron diffraction, magnetostatic measurements, M\"ossbauer spectroscopy, and dielectric measurements. The title compounds (trigonal, space group P321) display a helical magnetic order with signatures of frustration below TN ~24- 35 K where an anomaly of the dielectric permittivity is observed. The influence of the cationic substitutions and the nature of the magnetoelectric coupling is hereafter addressed.

The influence of intergranular interaction on the magnetization of the ensemble of oriented Stoner–Wohlfarth nanoparticles

The influence of interparticle interaction on the processes of magnetization reversal is considered for an ensemble of oriented Stoner–Wohlfarth nanoparticles. This is done through a solution of a kinetic equation describing the relaxation of the total magnetization to its equilibrium value in an effective mean field which includes a term proportional to the instantaneous value of the magnetization. It is shown that the interparticle interaction influences the temperature dependence of a coercive field. Under certain conditions, the presence of the interparticle interaction can lead to the formation of the so-called superferromagnetic state with the correlated directions of the magnetic moments of the particles. If the system is unable to come to the equilibrium during the time interval necessary to perform measurements, some measured quantities become dependent on the measurement time. It is shown that the blocking temperature Tb and the temperature dependence of coercive field at T<Tb are strongly dependent on a measurement time. At T>Tb, however, the coercivity, if exists, does not depend on the measurement time. The data of magnetostatic measurements, carried out on the (CoFeB)x–(SiO2)1−x nanogranular films with the concentration of ferromagnetic particles slightly lower than a percolation threshold, are in compliance with the results of the calculations.

Effect of Interaction in the Magnetization Reversal Relaxation of Superparamagnetic Granular CoFeB -SiO<sub>2</sub> Films

In order to study the magnetic interactions influence on the relaxation processes in superparamagnetic media, the magnetostatic measurements were carried out for the granular (CoFeB)x-(SiO2)1-x films with x values near percolation threshold. The observed temperature dependences of the coercivity for the samples magnetized along in-plane easy axis have shown two parts linear on with different inclination angles, which cross each other at the blocking temperature (Tb). The first part of the curve, which corresponds to the temperature range below Tb, depends on the measuring time and is related to the thermal activation nature of magnetization reversal process in the blocked superparamagnetic state. Second part of the curve, which corresponds to the temperature range above Tb, is practically independent on the measuring time and is related to existence of correlated state of superparamagnetic grains moments, i.e. to superferromagnetic state. The method of the magnetization reversal curves simulation based on the numerical solving of kinetic equation has been applied to explain the experimental results.

Influence of shape and chemical and phase compositions of iron-containing particles on microwave performance of composites with an insulating matrix

The structure and microwave magnetic properties of Fe powders grounded in argon or acetone and also of Fe-Si-C and amorphous Fe-Co-Si-C powders mechanically alloyed in argon are studied using X-ray diffraction, Mossbauer spectroscopy, granulometric and microscopic analyses, magnetostatic measurements, and microwave spectroscopy. The goal of investigation is to determine the influence of factors (shape, size, and chemical and phase compositions of grains) governing the microwave material parameters of composites based on these alloys in the frequency range 0.1–3.0 GHz. It is shown that the difference in the grain shape is the basic reason for the difference in the microwave permeability at low frequencies (3 GHz or lower). At higher frequencies, the magnetic properties are related to the skin effect and depend largely on the grain size. The differences in the microwave properties of the composites are not significant and are concealed by the above effects.