Magnetostrictive Stress Research Articles

A magnetic/force coupling assisted lithium-oxygen battery based on magnetostriction and piezoelectric catalysis of CoFe2O4/BiFeO3 cathode

The high energy density of Li−O2 batteries surpasses all existing batteries, and it holds the potential to emerge as the most outstanding solution for energy storage in the future. However, the insulated, insoluble discharge product (Li2O2) has impeded the practical applications. Conventional catalyst design based on electronic structure and interfacial charge transfer descriptors are incapable of overcoming these limitations of Li2O2. Herein, a magnetic/force coupling assisted Li−O2 battery based on magnetostrictive and piezoelectric catalysis with CoFe2O4/BiFeO3 core-shell structure cathode was established for the first time. An external magnetic field is introduced to produce a magnetostrictive stress on CoFe2O4, contributing to the piezoelectric electron hole transport by the generated piezoelectric potential energy with a built-in electric field based on the piezoelectric catalytic mechanism, and thus promoting the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics, and reducing the overpotential during charge/discharge. The magnetic/force coupling assisted Li−O2 battery equipped with the unique CoFe2O4/BiFeO3 cathode deliver an ultra-low charging platform of 3.49 V and an ultra-high discharge platform of 2.83 V. This unique magnetic/force assisted strategy provides an important insight into solving the high overpotential in metal-air battery systems.

Direct observation of magnetic domain walls in glass-coated submicronic amorphous wires

Results on the magnetic domain walls in rapidly solidified magnetostrictive and non-magnetostrictive amorphous submicronic wires are reported. Utilizing Lorentz transmission electron microscopy (LTEM) for the first time in this context, we have visualized and analyzed the domain walls in such ultra-thin amorphous wires. All the investigated samples display vortex magnetic domain walls, regardless of wire composition or diameter. In non-magnetostrictive wires, the domain walls maintain their structure and symmetry under varying magnetic field conditions. In contrast, magnetostrictive wires show an elongation of their domain walls upon magnetic field application, a response linked to the magnetoelastic coupling between magnetostriction and internal stresses induced during wire preparation. This study advances the understanding of magnetization reversal processes in amorphous submicronic wires. The insights gained are crucial for future developments in miniaturized magnetic devices.

Microstructure and Magnetic Properties of Nanocrystalline Fe60-xCo25Ni15Six Alloy Elaborated by High-Energy Mechanical Milling.

In the present work, the effect of Si addition on the magnetic properties of Fe60−xCo25Ni15Six (x = 0, 5, 10, 20, and 30 at%) alloys prepared by mechanical alloying was analyzed by X-ray diffraction and magnetic vibrating sample magnetometry and SQUID. The crystallographic parameters of the bcc-solid solutions were calculated by Rietveld refinement of the X-ray diffraction patterns with Maud software. Scanning electron microscopy (SEM) was used to determine the morphology of the powdered alloys as a function of milling time. It was found that the Si addition has an important role in the increase of structural hardening and brittleness of the particles (favoring the more pronounced refinement of crystallites). The resulting nanostructure is highlighted in accordance with the concept of the structure of defects. Magnetic properties were related to the metalloid addition, formed phases, and chemical compositions. All processed samples showed a soft ferromagnetic behavior (Hc ≤ 100 Oe). The inhomogeneous evolution of the magnetization saturation as a function of milling time is explained by the magnetostriction effective anisotropy and stress induced during mechanical alloying.

A High-Sensitivity Resonant Magnetic Sensor Based on Graphene Nanomechanical Resonator.

This paper presents a novel resonant magnetic sensor consisting of a graphene nanomechanical oscillator and magnetostrictive stress coupling structure, using Si/SiO2 substrate and Fe–Ga alloy, respectively. In this device, the deformation of the Fe–Ga alloy resulting from the external magnetic field changed the surface tension of the graphene, resulting in a significant change in the resonance frequency of graphene. Using the finite element analysis, it could be found that the response of the resonance frequency revealed a good linear relationship with the external magnetic field (along the x-axis) in the range of the 1 to 1.6 mT. By optimizing the sizes of each component of the magnetic sensor, such as the thickness of the Si/SiO2 substrate and the Fe–Ga alloy, and the length of the graphene, the sensitivity could even reach 834 kHz/mT, which is three orders of magnitude higher than conventional resonant magnetic devices. This provides a new method for highly sensitive and miniaturized magnetic sensors.

The effects of post-processing on longitudinal magnetostriction and core losses of high saturation flux density FeSiBC amorphous alloy ribbons and cores

Fe-based amorphous soft magnetic materials play an attractive role in energy saving and emission reduction due to low core losses. One of the problems is the acoustic noise resulting from magnetostriction during AC magnetization process. In this work, amorphous ribbons with a nominal composition of Fe81.5Si4B14C0.5 (at. %) were produced by planar flow casting and subjected to various postprocessing treatments. The influences of annealing conditions on the longitudinal magnetostriction, acoustic noise and core losses of the ribbons measured at low-field were studied. The effects of bending stress and epoxy impregnation and curing on medium frequency core losses of the alloy cores with different shapes were also investigated. It is shown that larger longitudinal magnetostriction of amorphous ribbons leads to higher acoustic noise emission from amorphous cores. Although the longitudinal magnetostriction was found to be reduced by applying a longitudinal magnetic field during annealing, the core loss was increased. The minimum longitudinal magnetostriction value at 1000 A/m is 7 ppm for ribbon annealed at 350 °C for 90 min. under an applied longitudinal magnetic field, while the lowest core losses at 1.4 T and 50 Hz is 0.213 W/kg for toroidal core annealed at 350 °C for 90 min. under an applied transverse magnetic field. The coupling between longitudinal magnetostriction and bending stress of amorphous ribbon results in an increase in core losses. Furthermore, extra stress was introduced after epoxy impregnation and curing, which also results in an increase in core losses. Thus, low longitudinal magnetostriction is important for stress insensitivity and soft magnetic properties.

Martensite Nucleation under Conditions of Austenite Superplasticity and External Magnetic Field

The thermodynamic conditions corresponding to the instability of the crystal lattice before the martensitic transformation are analyzed. The instability of the crystal lattice before the martensitic transformation can be crucial for the occurrence of such a phenomenon as superplasticity of the martensitic transformation. Phenomena arising in an instability state are considered, a theoretical analysis of possible structural states detected experimentally is carried out. The phenomenon of superplasticity of the martensitic transformation under tension in the Ms – Md interval and the effect exerted by the magnetic field in this interval are described. As a result of exposure to an external magnetic field in this temperature range, the resulting magnetostrictive stresses in ferromagnetically ordered austenite nanoclusters under superplastic conditions initiate the formation of martensite.

Origin of Magnetically Induced Optical Transmission of Magnetic Nanocomposite Films.

Herein, we present an investigation on the origin of the magnetically induced optical transmission of composite films comprised of polydimethylsiloxane and magnetic nanofillers via experiment and simulation. Structured and unstructured films were used in the study, which were fabricated with and without magnetic fields, respectively. Altered optical transmittance was observed from both types of films when they were subjected to an external magnetic field. Numerical analyses were performed to investigate the effect of the particle movement under magnetic field and the film magnetostriction on the film optical transmittance. The simulation results show that the changed light transmission under magnetic field is mainly due to a variation in the film thickness resulting from the film magnetostriction. The ellipsometric analysis results confirm the altered film thickness in response to the external magnetic field, and the measurements of the film magnetostrictive stresses validate that there is magnetostriction in the magnetic composite films. Additionally, it is indicated that there might be some relationship between the magnetically induced optical transmission and the film magnetostrictive stress under certain conditions.

Finite element formulation for implicit magnetostrictive constitutive relations

Magnetostrictive materials that couple mechanical and magnetic domains have been widely explored for use in sensors and actuators. These materials often exhibit a nonlinear material response under applied magnetic fields, which limits the use of linear constitutive models. Furthermore, the nonlinear constitutive relations tend to be implicit in nature. Hence, a finite element scheme that can handle the implicit relationship between the mechanical (stresses and strains) and magnetic (magnetic flux density and magnetic field) quantities is proposed in order to arrive at solutions to boundary value problems. In the proposed scheme, while the physical requirements of equilibrium and strain–displacement relation are satisfied point-wise, the constitutive relations hold in a weak integral sense. A fully coupled magnetostrictive plane stress rectangular element is developed based on the proposed scheme and its efficacy in arriving at solutions to coupled field boundary value problems is illustrated by subjecting the element to standard loading conditions.

Analytical methods for the radial electromagnetic vibration of stator in permanent magnet motors with an amorphous alloy core

The urgent demand for high efficiency of electrical machines leads to the preliminary application of amorphous alloy, however the accompanying vibration problem becomes more complex. The radial electromagnetic vibration of the amorphous stator core in a permanent magnet motor is analytically investigated in this paper. The magnetic field distribution approach considering the slotted effects and eccentricity is proposed and the air-gap magnetic flux density is validated by the finite element method. The magnetization and magnetostriction characteristics of the amorphous alloy are obtained. The dynamic models for the stator core including yoke sections and the tooth-yoke sections are respectively established. The Maxwell stress and magnetostriction stress are integrated in the magneto-mechanical coupling model. Dynamic responses in the stator core for different radii, position angles and times are analyzed. Vibrations of conventional core with silicon steel and amorphous core are compared. The spatial and temporal characteristics of the dynamic responses in the stator core are explored. The origins and corresponding weights in the electromagnetic vibration at different rotating speeds are revealed. Experiments of a modified permanent magnet motor equipped with the amorphous core are conducted. The theoretical results are validated well by experiments. Results demonstrate that the vibration level of the amorphous core is larger than the silicon steel core when other conditions are the same. Radial vibrations of the stator core are caused by the Maxwell stress, magnetostriction stress and their interaction effects. The weight of magnetostriction effects is improved with the increasing rotating speed. These findings provide an insight into the mechanism of electromagnetic vibration in amorphous stator core and can be helpful for the design of high-efficiency electrical machines.

A giant magnetoimpedance effect based nonvolatile Boolean logic gate

The biphase magnetic heterostructure (Ni/Fe20Ni45Co25Si2B8/micro-planarcoil/Fe20Ni45Co25Si2B8/micro-planar coil/Fe20Ni45Co25Si2B8/Ni) bonded with a pair of thin magnets shows an improved asymmetric and hysteretic giant magnetoimpedance (GMI) effect with respect to an external dc magnetic field. This is attributed to the modification of the soft amorphous magnetic alloy’s (Fe20Ni45Co25Si2B8) permeability by the hysteretic magnetostrictive stress from the neighboring magnetostrictive Ni layer besides the magnetostatic coupling. More importantly, nonvolatile logic gates, such as NOR and NAND, can be implemented with either a single GMI laminate or arrays. On one hand, after applying two sequential magnetic field pulses as the logic inputs to a single proposed laminate, the nonvolatile output voltages are positive high (logic 1) or positive low (logic 0) depending on the signs and magnitudes of pulses. On the other hand, after applying the magnetic field pulses parallel to the GMI laminates arrays, different logic functions can be programmed and realized at run-time. The integration of memory and logic functions enables the proposed GMI laminate to be a possible candidate for future computing systems beyond von Neumann architecture.

On ensuring joint tightness on the basis of technological induction

Introduction. Some theoretical and engineering aspects of sealing joints through magnetostriction, as well as the polarization of the sealed medium under the external induction are considered. Control of surface roughness of joined parts to increase the joint density when induced by an external magnetic field is studied. The creation of electromagnetic barriers for the migration of molecules of the sealed medium through a sealer is considered. The work objective is to validate the technological conditions for sealing movable joints in the cases described above. Materials and Methods. The conditions for ensuring the joint density are shown as a result of the contact problem solution and as a factor determined by the molecular-mechanical friction theory. Geometric, operational and tribological conditions of joint tightness are accepted. Damping properties of the fixed friction contact are determined by the molecular component. The theoretical and calculated analysis of the factors affecting the joint density is presented. Decrease in the smoothing depth, reduction of the ratio of transverse and longitudinal roughness steps, and increase in the contact area are indicated as the target results of the process preparation of the surfaces of the joint parts. Loss of tightness is defined as a specific transfer of molecules. They are transferred to the area of the joined surfaces or migrate freely through the sealer at the stages of sorption, diffusion and desorption. The predominance of any stage occurs when the entropy changes, and it is due to temperature and pressure. The schemes of sealing joints in the controlled magnetic field and of the dependence of magnetostriction and magnetostrictive stresses on the magnetic field strength are visualized. Research Results. The stability of sealers in highly volatile and gaseous media during their polarization and magnetization in an external field is experimentally investigated. In the former case, the magnetic induction vector was first oriented perpendicular to the longitudinal axis of the joint. A drop in the magnitude of the magnetic flux was observed when the compound was under the on-load operation for 268 hours. The total operating time of the joint was 1070 hours. If the magnetic induction vector was oriented longitudinally to the shaft axis, the operating time to the correction of the field strength was 87 hours. In the gas environment, the operating time of the connection to the adjustment of the tension was 187 hours with a total operating time of 935 hours. Discussion and Conclusions . The penetrating ability of pressurized media decreases in the “gas - vapor - liquid” series. It depends on the temperature at the joint contact. Depressurization can be traced through changes in the magnetic flux determined by the intrinsic magnetic permeability of the molecules of the sealed medium as they penetrate the interface surface. To increase tightness, it is required to suppress the activity of molecules. For this purpose, ionization and induction in the constant and alternating magnetic field with the intensity of <60 kA/m are used.

Features of Martensitic Transformation in Steel during Quenching in a Constant Magnetic Field

The data on the occurrence of martensitic transformation in steel under the action of a magnetic field were obtained by the electric resistivity method. The obtained data indicate the possibility of stress-assisted martensite formation in the temperature range of Ms-Md (in which superplasticity of austenite is observed). This possibility is due to the magnetic heterogeneity of austenite. Nanosized regions with a ferromagnetic order are present in the paramagnetic matrix. They can perceive the energy of the external magnetic field through the magnetostrictive stresses and change the fields of the elastic forces in the crystal lattice. All this leads to a decrease in the energy of formation of the nucleation center.

Magnetostriction of Fe-Ga coatings and their application in ultrasonic guided wave sensing

Fe83Ga17 (at. %) coatings with a thickness of 270-500 μm were prepared on 316L stainless steel by high velocity oxy-fuel spraying technology. The coatings exhibited a lamellar structure, and the magnetostriction reached 34.5 ppm. The magnetostrictive coatings were applied to electromagnetic acoustic transducers (EMATs), where the different bias magnetic fields and coating thicknesses were considered to examine the ultrasonic guided wave sensing capability and the detection sensitivity. The 180-kHz ultrasonic guided waves were captured from artificial defects and the pipe end under different bias magnetic fields. Among them, the EMATs exhibited the best sensing performance under a bias magnetic field of 255.7 Oe. Meanwhile, magnetostrictive stress induced the decrease of the magnetic permeability and the rearranged magnetic moment, resulting in a large strain sensitivity (dλ/dH). Because of the relatively good field sensitivities in magnetization and magnetostriction, the EMATs using Fe83Ga17 coating with a thickness of 500 μm exhibited better detection sensitivity than that of 300 μm. This work provides a good prospect of Fe-Ga alloy coatings applied in non-destructive testing.

Inverse magnetostrictive stress sensors based on crossed pinned CoFeB/MgO/CoFeB tunnel junctions

The usage of double pinned magnetic CoFeB/MgO/CoFeB tunnel junctions with noncollinear magnetizations as sensors of mechanical stress is shown. For this purpose, tunnel magnetoresistive (TMR) stacks with MnIr based pinning of both electrodes have been prepared. By using different MnIr thicknesses, we were able to realize noncollinear magnetizations. A series of annealing steps with a field perpendicular to the initial exchange bias direction have been performed in order to find the optimum thermal treatment for the best performance of the sensors. On these systems, bending experiments were completed which, show the suitability of our double-pinned TMR elements as stress sensors and their performance in differentiating tensile and compressive stress.

Enhanced permittivity and permeability of (1-y)(Mg0.95Zn0.05)2TiO4-yMg0.95Zn0.05Fe2O4 ceramics

We report the preparation of the solid-solutions (1-y)(Mg0.95Zn0.05)2TiO4-yMg0.95Zn0.05Fe2O4 (y = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) by traditional solid-state reaction and systematically study their phases, morphologies, and magnetodielectric properties. The giant dielectric constants are observed at low frequency in the ceramics, with y > 0.5 when the sintering temperature exceeds 1200 ℃. The highest relative permittivity ε' of 9.98 × 103 at 30 kHz and the largest squareness ratio of 0.89 for the magnetic hysteresis loop are achieved in 0.1MZT-0.9MZF. In addition, the enhanced initial permeability μi of ∼70 is obtained in 0.3MZT-0.7MZF due to its large grain size and probably the smaller magnetostriction and internal stress caused by lower relative density. All the results indicate that our solid-solutions with y > 0.5 can considerably improve the dielectric and magnetic properties, providing more advantages than the simple bi-phasic compounds in the applications for novel electronic devices.

A Resonant Magnetic Field Sensor With High Quality Factor Based on Quartz Crystal Resonator and Magnetostrictive Stress Coupling

A resonant magnetic field sensor is developed by using a piezoelectric quartz crystal double-ended tuning fork (DETF), two FeGa thin plates, and four quartz spacers. The double ends of the DETF are bonded to the ends of the magnetostrictive thin plates through four spacers with adhesive, allowing the magnetostrictive force to be converted into the longitudinal force in the DETF which leads to an increase of the resonant frequency of the DETF. This design brings the advantage of field-independent damping, i.e., the quality factor (Q-factor) of the sensor is found to be independent on the dc field, with an average value of about 3318 in the air due to the low internal loss in quartz. After an initially slow increase before the field reaching ~50 Oe, the resonant frequency of the sensor increases linearly with the increase of the applied dc field before reaching 280 Oe. The total frequency shift, sensitivity of the frequency shift per magnetic field, and field resolution in the linear region are 2.12% (~808.3 Hz), 3.5 Hz/Oe and 8 mOe, respectively. The results demonstrate a possibility and promising to realize a highly sensitive magnetic sensor with high-Q-factor quartz crystal as well as direct digital frequency output.

Stress Analysis of Inverter-Fed Induction Motor Considering Anisotropic Magnetization and Magnetostrictive Properties

Inverter-fed induction motors generate large vibration and noise because of the Maxwell electromagnetic stress between stator and rotor, magnetostrictive stress of silicon steel and the harmonics in load current. On the vibration reduction study of motor cores, many researchers kept their eyes on control strategy. However, they did not compute stress of inverter-fed induction motor under sinusoidal and harmonic excitations. The nonoriented silicon steel in motor cores shows remarkably anisotropic magnetization and magnetostrictive properties under sinusoidal and harmonic excitations. Thus, in order to compute motor stress accurately, anisotropic magnetic properties must be considered. First, anisotropic property of silicon steel under sinusoidal and harmonic excitations is tested to support the stress computation. Then, an electromagneto-mechanical coupled model for motors considering anisotropic magnetization and magnetostrictive properties is proposed and stress distribution of motor cores is calculated. Finally, the frequency spectrum of the stress is analyzed to provide the theoretical basis for further research of inverter-fed induction motor vibration and noise reduction.

The change of domain structure of the amorphous microwire of Fe73.5Cu1Nb3Si13.5B9 composition under thermal treatment

The investigation on domain structure evolution under variation of magnetostriction, phase composition and internal stresses was provided. Glass-coated amorphous microwires of Fe73.5Cu1Nb3Si13.5B9 composition with positive magnetostriction were studied. The decrease of internal stresses and controlled crystallization leading to changes in the phase composition and reduction of magnetostriction were observed under different thermal treatment. The domain structure of the as-prepared and annealed microwires was studied by the method of magneto-optical indicator films. The estimation of the domain size was realized by Fourier transform from the domain contrast of magneto-optical images. The regularities of the influence of thermal treatment on the magnetic domain structure of microwires have been estimated.

Ferromagnetically ordered clusters in austenite as the areas of martensite formation

In this research, the peculiarities of the magnetic state of austenite of carbon steels were studied. The effect of an external magnetic field on the process of martensitic transformation is discussed. It is shown that there are nanoscale regions with ferromagnetic order in austenite. These regions are possible locations for the nucleation of martensite. In the case of magnetic field influence, the ferromagnetic clusters are able to perceive the energy of the external magnetic field by magnetostrictive stresses (which reduce the energy of martensite formation). Ferromagnetically ordered clusters have a certain critical size, below which the single-domain region becomes unstable. The dependence of the critical size of the ferromagnetic cluster on the intensity of the magnetic field was observed. This dependence shows that the higher the intensity of the field, the smaller the size of the clusters that can remain stable. Thus, a strong magnetic field increases the amount of ferromagnetic nanoclusters (consequently, the number of the nucleation centers of martensite increases). The results of the research allow estimating more accurately the effect of a magnetic field on decreasing the formation energy of a nucleation center.

Magnetically Controlled Saturable Reactor Core Vibration Under Practical Working Conditions

In order to seek new vibration reduction method for magnetically controlled saturable reactors (MCSRs), this paper studies the stress characteristic which is the inherent reason of vibration and noise. Under the practical working condition, dc and ac excitations make iron cores work in a magnetic saturation state. Meanwhile, the stress in reactor cores always exists and influences on magnetic properties of the core material. Because the core material shows different magnetization and magnetostrictive properties under dc bias and stress, a database of magnetization and magnetostrictive curves of silicon steel under different tensile stresses with different dc bias excitations is tested. Based on the measured constitutive relations, an electromagneto-mechanical two-way coupled numerical model for MCSRs is presented. Vibrations considering magnetostrictive effect, electromagnetic force effect, and the combination of them are calculated to compare the influence of the two forces on MCSR vibration. From the computation results, it can be seen that the total vibration stress is not a simple superposition of electromagnetic stress and magnetostrictive stress. Finally, vibration stress of an MCSR prototype under working conditions is tested to prove the validity of the proposed model.