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This paper presents a computationally efficient constitutive model for magnetostrictive materials. High computational efficiency is achieved through the use of local linearization (about easy axes) and discrete energy-averaging techniques. The model is applied to iron-gallium alloys (Galfenol) and tested for different magnetic field orientations relative to the easy axes. It is observed that the model accurately predicts both sensing and actuation characteristics while reducing the computation time by a large factor (> 1000 times) when compared to the nonlinear energy minimization models. Furthermore, the average error observed in λ – H and B – H curves is less than 3.5% with the error increasing at magnetic field orientations farther from easy axes, particularly at large magnetic field values. Finally, the model is integrated with a finite element framework to predict the response of a Galfenol rod transducer system, and parametric studies are performed for different current and prestress conditions to optimize the device performance. [ABSTRACT FROM AUTHOR]

A two-dimensional constitutive model based on micromechanical domain rotation events is presented in this work to demonstrate the nonlinear actuator behavior of magnetostrictive materials, in particular, Galfenol. The model constructed upon thermodynamic principles accounts back fields which resist or aid the domain rotation events inside a grain due to external magnetomechanical loading. The developed model is then incorporated into the polygonal finite element technique that combines Voronoi-based discretization with the hybrid finite element method. In this approach, the stress and magnetic flux density are treated as approximate functions inside the element, but the mechanical displacement and magnetic potential, which act as degrees of freedom, are defined only along the element boundary. This approach allows each randomly generated Voronoi polygon in the plane discretization to act as a single finite element mimicking an individual magnetomechanical grain in a polycrystalline Galfenol, eliminating the need for further subdiscretization of the Voronoi polygon. This coupled framework simulates the nonlinear actuator characteristics of the magnetostrictive material under complex magnetomechanical loading conditions in line with the experimental observations reported in the literature. [ABSTRACT FROM AUTHOR]

The effect of crystal orientation and grain alignment on the properties of magnetostrictive materials was investigated in TbFe2 alloys prepared via solidification under different high magnetic field conditions. The magnetostrictive property and magnetization behavior of the alloys were studied. The results revealed that the alloys that are oriented along the easy magnetization axis exhibit better magnetostrictive property in the low-field intensity region (than in the high-field intensity region). However, in the high-field intensity region, regular alignment of grains in the magnetization direction is essential for continued improvement in the magnetostrictive property of the alloys. If the magnetic phases of the TbFe2 alloy are oriented along the easy magnetization axis and the grains of the magnetic phases are aligned regularly along the direction of magnetization, the alloy will exhibit excellent magnetostriction property. This study may serve as a reference for the preparation of high performance rare-earth iron-based magnetostrictive materials. [ABSTRACT FROM AUTHOR]

A characteristic modulation of the magnetic domain structure on the (001) plane of an Fe–12.8 at. % Ga alloy single crystal under tensile stress was observed by magneto-optic Kerr effect microscopy. The magnetic domain structure under zero applied stress was composed of magnetic domains with magnetizations in four types of <100> magnetic easy directions on the (001) plane, which were separated by straight 90° domain walls and stair-like 180° domain walls. When a tensile stress of 11.4 MPa was applied parallel to the [010] direction, these 90° domain walls disappeared to release the tensile stress. A stripe domain structure that was composed of straight 180° domain walls parallel to the tensile stress direction was thus formed by the inverse magnetostrictive effect. Young's modulus of the alloy below the applied 11.4 MPa tensile stress was estimated to be 32 GPa, which is 57% smaller than the corresponding value above that tensile stress value. Consequently, a significant reduction in Young's modulus is caused by the characteristic modulation of the magnetic domain structure that occurs as a result of the inverse magnetostrictive effect. [ABSTRACT FROM AUTHOR]

We studied the depth dependent magnetization profile of the magnetostrictive Co thin film layer in a (PbMg0.33Nb0.67)1-x:(PbTiO3)x (PMN-PT) (011)/Ta/Co/Ta structure under both zero and nonzero applied electric field using polarized neutron reflectometry. Application of an electric field across the PMN-PT substrate generates a strain, which rotates the magnetization of the Co layer consistent with the Villari effect. At low magnetic fields (near remanence and coercive field conditions), we find that the depth dependent magnetization profile is non-uniform, under both zero and nonzero applied electric fields. These variations are attributable to the depth dependent strain profile in the Co film, as determined by finite element analysis simulations. [ABSTRACT FROM AUTHOR]

We report on the enhanced magnetostrictive properties of nanocrystalline Dysprosium (Dy3+) substituted iron-rich cobalt ferrites (Co0.8Fe(2.2-x)DyxO4, referred to as CFDO). The CFDO samples with a variable Dy concentration (x = 0.000–0.075) were synthesized by the sol-gel auto-combustion method. The phase purity and crystal structure were confirmed from X-ray diffraction analyses coupled with Rietveld refinement. Surface morphology analysis using scanning electron microscopy imaging indicates the agglomerated magnetic particles with a non-uniform particle size distribution, which is desirable to transfer the strain. The magnetostriction coefficient (λ11) measurements indicate that the CFDO with Dy concentration x = 0.025 exhibits the highest strain sensitivity, (dλ/dH) ∼1.432 nm/A (for H ≤ 1000 Oe). On the other hand, the magnetostriction coefficient (λ12) measurements indicate that the Dy concentration x = 0.075 exhibits the larger (dλ/dH) ∼ 0.615 nm/A (for H ≤ 1000 Oe). The maximum λ11value of 166 ppm (at H = 3300 Oe) was observed for a compound with Dy concentration x = 0.050. Magnetization measurements indicate that the saturation magnetization and coercivity of CFDO samples are dependent on the Dy3+content; the highest value of squareness ratio of 0.424 was observed for x = 0.050. The interplay between strain sensitivity (dλ/dH) and instantaneous susceptibility (dM/dH), as derived from magnetostriction and magnetization results, demonstrates that these CFDO materials may be useful for developing torque/stress sensors, as a constituent magnetostrictive phase for making the magnetoelectric composite materials and thus suitable for magnetoelectric sensor applications. [ABSTRACT FROM AUTHOR]

This paper reports the effect of the film thickness on the magnetostrictive behavior of (Fe,Co) rich Tb-(Fe,Co) films grown on Si <100> by electron beam evaporation. Magnetostriction was found to decrease with an increase in film thicknesses. To understand the variation of magnetostriction with the film thickness, detailed structural, microstructural, magnetization, and magnetic microscopy studies were carried out. X-ray diffraction studies indicated the presence of two phases, viz., Tb2 (Fe, Co)17 and Fe-Co phases, for all the films. With the increase in the film thickness, the peak intensity of the Tb2 (Fe, Co)17 phase decreased and that of the Fe-Co phase increased. Magnetization studies showed the presence of strong in-plane anisotropy for all the films. In addition to this, the presence of the out-of-plane component of magnetization was also observed for the films grown with higher thicknesses. This anisotropic behavior was also validated through magnetic microscopy studies carried out along the in-plane and out-of-plane directions employing magneto-optic Kerr microscopy and magnetic force microscopy, respectively. The decrease in magnetostriction was explained on the basis of dual phase formation and complex interplay between the in-plane and out-of-plane magnetic anisotropies present in the film. [ABSTRACT FROM AUTHOR]

Lead-free multiferroic ceramics consisting of (1-x) 80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3 (BNTBKT)-xNi0.8Zn0.2Fe2O4 (NZFO) (x=0, 0.15, 0.25, 0.35, and 0.45) were synthesized by the in situ sol-gel method. The structural, ferroelectric, piezoelectric, ferromagnetic, and magnetoelectric (ME) properties were measured as a function of the NZFO content x. The results showed that the coexistence of BNT-BKT and NZFO phases and the presence of the morphotropic phase boundary in the BNT-BKT phase with a high piezoelectric coefficient d33 (~131 pC/N) were confirmed. The composites exhibited a homogeneous microstructure and well-combined interfaces between the magnetostrictive and piezoelectric phases, as well as an improved ME response. The largest ME voltage coefficient (αME) of 42.41 mV/cm Oe was achieved for the 0.65(BNT-BKT)-0.35NZFO composite, which is in fact the highest one reported so far for lead-free particulate ME composites fabricated via in situ processing. [ABSTRACT FROM AUTHOR]

In this work, a sensitive tool to detect magnetic nanoparticles (Fe3O4) based on a non-linear Giant Magnetoimpedance (GMI) effect is presented. The GMI sensor is designed with four nearly zero magnetostrictive ribbons connected in series and was analysed as a function of a constant external magnetic field and exciting frequency. The influence of the magnetic nanoparticles deposited on the ribbon surface was characterized using the first (fundamental) and second (non-linear) harmonics of the magnetoinductive voltage. The results show a clear enhancement of the sensor response in the high magnetic field region (H=1.5 kA/m) as a consequence of the stray field generated by the magnetic nanoparticles on the GMI ribbons' surface. The highest sensitivity ratios are obtained for the non-linear component in comparison with the fundamental response. The results open a new research strategy in magnetic nanoparticle detection. [ABSTRACT FROM AUTHOR]

A multiferroic magnetic field sensor capable of producing an output for threshold magnetic fields has been fabricated and characterized. The sensor consists of a trilayer composite of piezoelectric X-cut lanthanum gallium tantalate and magnetostrictive Metglas placed inside a solenoid and a wide-band amplifier. The composite plays two distinct roles in the device; it forms the feedback loop of an oscillator and sets the frequency of sustained oscillations. The sensor generated an output of 2.5V at the longitudinal acoustic resonance frequency of 87.5 kHz for the trilayer for DC magnetic fields H=0.3 to 50 Oe parallel to the composite plane. The device functions as a threshold magnetic field sensor for this H-interval, and the threshold ON and OFF H-values for an ac voltage output could be controlled electronically or with a proper choice of the ferromagnetic phase in the composite. [ABSTRACT FROM AUTHOR]

Comparative studies have been made to understand the role of different crystallographic site preferences of the substituted non-magnetic divalent metal ions in the magnetostrictive properties of cobalt ferrite, by substitution of Zn2+ and/or Mg2+ for Fe3+ in CoMgxFe2-xO4, CoZnxFe2-xO4, and CoMgx/2Znx/2Fe2-xO4 (0.0≤x≤0.2). Detailed Raman spectral and magnetic characterizations are made to extract the information on the tetrahedral/octahedral site preferences of Zn and Mg in the spinel lattice of cobalt ferrite. The structural, microstructural, magnetic, Raman spectral, and magnetostrictive parameters of the studied compositions show distinguishable variations for x<0.1 and x ≥0.1. Co-substitution of a small amount of Mg and Zn for Fe in CoMgx/2Znx/2Fe2-xO4 (x < 0.1) showed relatively larger strain sensitivity, [dk/dH]max (-2.6 ×10-9mA-1 for x=0.05), higher than that for the Mg-substituted samples (-2.05 × 10-9mA-1 for x=0.05) and comparable to that for the Zn-substituted samples (-2.47 × 10-9mA-1 for x=0.05), without much drop in the maximum value of magnetostriction, kmax (-189 ppm for x=0.05) compared to that for the unsubstituted counterpart (-221 ppm). The results show that it is possible to obtain high strain sensitivity (at fields <50 kA/m), along with high magnetostriction strain at low magnetic fields (∼250 kA/m), by tuning the distribution of the substituted cations in the tetrahedral and octahedral sites of the cobalt ferrite lattice. [ABSTRACT FROM AUTHOR]

This article introduces a new method to realize the 180° magnetic moment reversal of a ferromagnetic and ferroelectric heterostructure through electrostriction-induced magnetic anisotropy. A rectangular magnetic FeAl alloy island with a large magnetostrictive coefficient on a PZN (011) substrate was adopted in our investigation through micromagnetic simulation. Using electrostriction along the [11-1] and [1-11] directions, the magnetic moment was rotated from the long axis of the rectangular island to the direction of the strain and finally reversed to the opposite direction despite the strain sequence. The magnetic moment can be oriented to a certain direction through a certain sequence of strain if a several hundred Oe magnetic field is applied along the short axis of the island. The suitable stress-induced magnetic anisotropy energy and external magnetic field were also investigated. In consideration that a high magnetic field along the short axis leads to small thermal stability of the magnetic moment, the suitable value of stress-induced anisotropy energy is around the critical value where the stress can reverse the magnetic moment without a magnetic field. We compared the stress-induced magnetic reversal processes for same-sized semicircular, elliptical, and rectangular islands and found that the semicircular island can be more easily reversed. [ABSTRACT FROM AUTHOR]

The direct nonlinear magnetoelectric (ME) effect and the magnetostriction of piezoelectric CsCuCl3 single crystals were comprehensively studied over a wide temperature range in stationary magnetic fields of up to 14 T. The direct nonlinear ME effect measurements were also performed in pulsed magnetic fields up to 31 T, at liquid helium temperature in the antiferromagnetic (AF) state for the crystallographic direction in which effect has the maximum value. The nonlinear ME effect was quadratic in the paramagnetic state for the whole range of magnetic fields. In the AF state the phase transition between different configurations of spins manifested itself as plateau-like peculiarity on the nonlinear ME effect. The nonlinear ME effect was saturated by the phase transition to the spin-saturated paramagnetic state. Two contributions to the nonlinear ME effects in CsCuCl3 were extracted from the experimental data: the intrinsic ME effect originated from the magnetoelectric interactions, and the extrinsic one, which resulted from a magnetostriction-induced piezoelectric effect. [ABSTRACT FROM AUTHOR]

A theoretical model quantifying the effect of temperature variations on the magnetic properties and static and dynamic behavior of the straintronics magnetic tunneling junction is presented. Four common magnetostrictive materials (Nickel, Cobalt, Terfenol-D, and Galfenol) are analyzed to determine their temperature sensitivity and to provide a comprehensive database for different applications. The variations of magnetic anisotropies are studied in detail for temperature levels up to the Curie temperature. The energy barrier of the free layer and the critical voltage required for flipping the magnetization vector are inspected as important metrics that dominate the energy requirements and noise immunity when the device is incorporated into large systems. To study the dynamic thermal noise, the effect of the Langevin thermal field on the free layer's magnetization vector is incorporated into the Landau-Lifshitz-Gilbert equation. The switching energy, flipping delay, write, and hold error probabilities are studied, which are important metrics for nonvolatile memories, an important application of the straintronics magnetic tunneling junctions. [ABSTRACT FROM AUTHOR]

A positive magnetostrictive single layer (CoFe) and top-pinned spin-valve structure with positive magnetostrictive free (NiFe) and pinned (CoFe) layers were deposited on flexible polyethylene terephthalate film to investigate the changes in the magnetic properties in flexible environments, especially with a repetitive bending process. It was found that the stress, applied by repetitive bending, changes significantly the magnetic anisotropy of both layers in a single and spin-valve structure depending on the direction of applied stress. The changes in magnetic anisotropy were understood in terms of the inverse magnetostriction effect (the Villari effect) and the elastic recovery force from the flexibility of the polymer substrate. Repetitive bending with tensile stress transverse (or parallel) to the magnetic easy axis was found to enhance (or reduce) the magnetic anisotropy and, consequently, the magnetoresistance ratio of a spin-valve. The observed effects of bending stress in this study should be considered for the practical applications of electro-magnetic devices, especially magneto-striction sensor. [ABSTRACT FROM AUTHOR]

Results on the analysis of the magnetoelastic and magnetostatic contributions in the total free energy of nearly zero magnetostrictive amorphous glass-coated nanowires prepared by means of rapid solidification are reported. The comparative study shows that both terms have values of the same order. However, the magnetostatic term is the most important one over a wide range of dimensions, being responsible for the domain structure formation and for the overall magnetic behavior of the investigated nanowires, which mainly consists in the appearance of an axial magnetic bistability. Even in the thinnest samples, the magnetostatic contribution is essential, in spite of an important magnetoelastic one, too. Calculated results agree with the experimental hysteresis loop data. The results are a key for understanding and controlling the magnetization processes in these novel nanowires. [ABSTRACT FROM AUTHOR]

We develop high power magnetostrictive vibration power generator for battery-free wireless electronics. The generator is based on a cantilever of parallel beam structure consisting of coil-wound Galfenol and stainless plates with permanent magnet for bias. Oscillating force exerted on the tip bends the cantilever in vibration yields stress variation of Galfenol plate, which causes flux variation and generates voltage on coil due to the law of induction. This generator has advantages over conventional, such as piezoelectric or moving magnet types, in the point of high efficiency, highly robust, and low electrical impedance. Our concern is the improvement of energy conversion efficiency dependent on the dimension. Especially, force factor, the conversion ratio of the electromotive force (voltage) on the tip velocity in vibration, has an important role in energy conversion process. First, the theoretical value of the force factor is formulated and then the validity was verified by experiments, where we compare four types of prototype with parameters of the dimension using 7.0 × 1.5 × 50mm beams of Galfenol with 1606-turn wound coil. In addition, the energy conversion efficiency of the prototypes depending on load resistance was measured. The most efficient prototype exhibits the maximum instantaneous power of 0.73W and energy of 4.7 mJ at a free vibration of frequency of 202 Hz in the case of applied force is 25 N. Further, it was found that energy conversion efficiency depends not only on the force factor but also on the damping (mechanical loss) of the vibration. [ABSTRACT FROM AUTHOR]

Iron is a well-utilized material in structural and magnetic applications. This does not mean, however, that it is well understood, especially in the field of magnetostriction. In particular, the rhombohedral magnetostriction of iron, λ111, is anomalous in two respects: it is negative in sign, in disagreement with the prediction of first principles theory, and its magnitude decreases with increasing temperature much too rapidly to be explained by a power law dependence on magnetization. These behaviors could arise from the location of the Fermi level, which leaves a small region of the majority 3d t2g states unfilled, possibly favoring small internal displacements that split these states. If this view is correct, adding small amounts of Co to Fe fills some of these states, and the value of λ111 should increase toward a positive value, as predicted for perfect bcc Fe. We have measured the magnetostriction coefficients (λ111 and λ100) of pure Fe, Fe97Co3, and Fe94Co6 single crystals from 77K to 450 K. Resonant ultrasound spectroscopy has been used to check for anomalies in the associated elastic constants, c44 and c'. The additional electrons provided by the cobalt atoms indeed produced positive contributions to both magnetostriction constants, λ111 and λ100, exhibiting an increase of 2.8 × 10-6 per at.% Co for λ111 and 3.8×10-6 per at.% Co for λ100. [ABSTRACT FROM AUTHOR]

This paper presents two-dimensional magnetostriction of electrical steel sheet under vector magnetic characteristic. In conventional measurement method using Single Sheet Tester, the magnetic flux density, the magnetic field strength, and the magnetostriction have been measured in one direction. However, an angle between the magnetic flux density vector and the magnetic field strength vector exists because the magnetic property is vector quantity. An angle between the magnetic flux density vector and the direction of maximum magnetostriction also exists. We developed a new measurement method, which enables measurement of these angles. The vector magnetic characteristic and the two-dimensional magnetostriction have been measured using the new measurement method. The BH and Bλ curves considering the angles are shown in this paper. The analyzed results considering the angles are also made clear. [ABSTRACT FROM AUTHOR]

The spin configuration and spontaneous magnetostriction λ111 of TbxDy0.92-xNd0.1(Fe0.8Co0.2)1.93 (0.20⩽x⩽0.60) alloys have been investigated. The easy magnetization direction (EMD) at room temperature was observed towards the (111) axis when 0.40⩽x⩽0.60, accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ111, which increases from 1640 ppm for x=0.40 to 1900 ppm for x=0.60. The strong (111)-oriented pseudo 1-3 particulate composite was fabricated by embedding and aligning particles in a passive epoxy matrix under an applied magnetic field. An enhanced magnetostrictive effect, the large low-field magnetostriction, λa, as high as 480 ppm at 3 kOe, was obtained for the sample of x=0.40, in an excess of 75% of its polycrystalline alloy although it only contains 27 vol.% alloy particles. This enhanced effect can be attributed to its low magnetic anisotropy, anisotropic magnetostrictive nature (e.g., λ111 ≠λ100, (111)EMD), chain structure, and the (111)-textured orientation. In addition, we give a direct experimental support that the (111)EMD of particle and the strong (111)-textured orientation are the crucial factors to realize the enhanced magnetostrictive effect in 1-3 particulate composites. [ABSTRACT FROM AUTHOR]

The (Tb0.3Dy0.7Fe1.9)1-x(Tb0.15Ho0.85Fe1.9)x alloys were prepared in an arc furnace under high purity argon. The as-cast samples wrapped in Mo foil were sealed in a silica tube filled with high purity argon and were homogenized at 1000 °C for 1 day and at 950 °C for 5 days. Then, the homogenized specimens with 5mm in diameter and 8mm in length were annealed under the magnetic field of 320 kA/m. The static measurement of magnetostriction (λ//, λ⊥) was made by standard strain gauge, and the magnetization M was measured by a vibrating sample magnetometer. It is found that the main phase of annealed (Tb0.3Dy0.7Fe1.9)1-x(Tb0.15Ho0.85Fe1.9)xalloys is the (Tb,Dy,Ho)Fe2 phase with the MgCu2-type structure. The magnetostriction λ// and magnetization M of (Tb0.3Dy0.7Fe1.9)1-x(Tb0.15Ho0.85Fe1.9)x alloys increases with increasing x from x=0.1 to x=0.3 when H<240 kA/m. The hysteresis becomes small with increasing x when x⩽0.3. For magnetically annealed rod alloys, the magnetostriction markedly increases and reaches 1080 × 10-6> for x=0.3 when H=240 kA/m. [ABSTRACT FROM AUTHOR]

This paper presents a fully coupled, nonlinear electromagnetic-mechanical-thermal model for Terfenol-D devices which include active magnetostrictive materials and passive components. The model includes two parts: (1) a material-level discrete energy-averaged model (DEAM) to describe the magnetomechanical coupling and thermal effect of Terfenol-D and (2) a system-level finite element model formulated in weak form using Maxwell's equations, Newton's law, and heat transfer equations. The objective is to describe the electromagnetic, mechanical, and thermal dynamics of the device. The system finite element model is constructed in COMSOL Multiphysics, and the nonlinear behavior of Terfenol-D is coupled through lookup tables generated by the DEAM. Preliminary results of the output capacity of a Terfenol-D actuator with respect to ambient temperature are presented in terms of blocked force, free displacement, and output power. The blocked force and free displacement decrease by 8.0% and 29.8%, respectively, for a 12A (RMS) excitation current, as the temperature increases from 20 °C to 180°C. One of the key contributions of this study is that it accounts for both the temperature-dependent Terfenol-D properties and the thermal effects of surrounding passive systems. [ABSTRACT FROM AUTHOR]

Magnetostrictive bending cantilevers are applicable for wirelessly measuring physical quantities such as pressure and strain. Exploiting the DE-effect, the resonance frequency of the cantilevers is shifted because of a change in the magnetic biasing field. The biasing field, in turn, depends on the applied pressure or strain, respectively. With a view to the application as a reliable sensor, maximum sensitivity but minimum hysteresis in the biasing field/resonance frequency dependence is preferred. In this contribution, monomorph bending cantilevers fabricated using magnetostrictive Fe49Co49V2 and Metglas 2605SA1 are investigated regarding their applicability for future sensors. For this purpose, the biasing field-dependent polarization of the magnetostrictive materials and bending of the cantilevers are determined. Furthermore, a setup to magnetically bias the cantilevers and determine the bending resonance frequency is presented. Here, the resonance frequency is identified by measuring the impulse response employing a laser Doppler vibrometer. The measurement results reveal that cantilevers made of Fe49Co49V2 possess a distinct hysteretic behaviour at low magnetic biasing field magnitudes. This is ascribed to the polarization and bending hysteresis. Cantilevers fabricated using Metglas 2605SA1 feature a lower resonance frequency shift compared to cantilevers with Fe49Co49V2, which would result in a lower sensitivity of the sensor. However, their resonance frequency hysteresis is almost negligible. [ABSTRACT FROM AUTHOR]

A dc magnetoelectric sensor operating in ac voltage driving mode is developed based on a piezoelectric-magnetostrictive heterostructure having four thickness-polarized Pb(Zr, Ti)O3 piezoelectric plates bonded symmetrically on a length-magnetized Tb0.3Dy0.7Fe1.92 magnetostrictive plate to give an electrically parallel input and an electrically series output. The dc magnetic field sensing in the sensor is evaluated theoretically and experimentally and is found to originate from a unique ac voltage-driven, dc magnetic field-tuned resonance dc magnetoelectric effect in the heterostructure. An interestingly high, linear, and negative ac voltage-controlled dc magnetic field sensitivity of -1.3 mV/Oe/V is obtained in a broad range of dc magnetic field of 0-400 Oe by referencing an ac voltage of ⩽5V peak amplitude and 116 kHz frequency at the input of the heterostructure. [ABSTRACT FROM AUTHOR]

Vibration based power generation technology is utilized effectively in various fields. Author has invented novel vibrational power generation device using magnetostrictive material. The device is based on parallel beam structure consisting of a rod of iron-gallium alloy wound with coil and yoke accompanied with permanent magnet. When bending force is applied on the tip of the device, the magnetization inside the rod varies with induced stress due to the inverse magnetostrictive effect. In vibration, the time variation of the magnetization generates voltage on the wound coil. The magnetostrictive type is advantageous over conventional such using piezoelectric or moving magnet types in high efficiency and high robustness, and low electrical impedance. Here, author has established device configuration, simple, rigid, and high power output endurable for practical applications. In addition, the improved device is lower cost using less volume of Fe-Ga and permanent magnet compared to our conventional, and its assembly by soldering is easy and fast suitable for mass production. Average power of 3 mW/cm³ under resonant vibration of 212 Hz and 1.2G was obtained in miniature prototype using Fe-Ga rod of 2 × 0.5× 7mm³. Furthermore, the damping effect was observed, which demonstrates high energy conversion of the generator. [ABSTRACT FROM AUTHOR]

We have investigated for the first time the combined effect of current and stress on the giant magnetoimpedance characteristics of vanishing-magnetostrictive Co-rich microwires at microwave frequency. As the current-annealed wire is subject to certain tensile stress, one can observe a drastic transformation of field dependence of magnetoimpedance (MI) profiles from smooth shape of a broad peak to deformed shape of a sharp peak with the emergence of a kink on each side. It follows that three different regions-core, inner, and outer shell-have been formed by the combined effect of Joule-annealing, current generated magnetic field, and the tensile stress. A critical field sees a drop of field sensitivity from outer to inner shell and shifts to lower value with increasing annealing current. We successfully adapted our core-shell model to a core-shell-shell model by designating different anisotropy fields for each region to satisfactorily resolve the unique double-curvature shaped peaks in the field derivative MI profiles. [ABSTRACT FROM AUTHOR]

Magnetostrictive behaviors under rotating magnetic fields are investigated for bcc(001) single-crystal films of Fe100-x-Six(x=0, 6, 10 at.%). The magnetostriction observation directions are along bcc[100] and bcc[110] of the films. The magnetostriction waveform varies greatly depending on the observation direction. For the observation along [100], the magnetostriction waveform of all the films is bathtub-like and the amplitude stays at almost constant even when the magnetic field is increased up to the anisotropy field. On the other hand, the waveform along [110] is triangular and the amplitude increases with increasing magnetic field up to the anisotropy field and then saturates. In addition, the waveform of Fe90Si10 film is distorted triangular when the applied magnetic fields are less than its anisotropy field. These magnetostrictive behaviors under rotating magnetic fields are well explained by employing a proposed modified coherent rotation model where the anisotropy field and the magnetization reversal field are determined by using measured magnetization curves. The results show that magnetocrystalline anisotropy plays important role on magnetostrictive behavior under rotating magnetic fields. [ABSTRACT FROM AUTHOR]

Magnetostrictive amorphous ribbons are widely used in electronic article surveillance as well as for magnetoelastic sensors. Both applications utilize the fact that the ribbons' resonant frequency can be read out remotely by applying external magnetic AC fields. This paper proposes a magnetomechanical model to simulate the dynamics of such ribbons. The goal was to only use general material properties as input parameters, which are usually denoted in the data sheet of amorphous metals. Thus, only the magnetization curve at zero stress has to be gained via measurement. The magnetization under stress is calculated thereof. The equation of motion for a longitudinally oscillating ribbon is derived and coupled to Maxwell's equations for magnetostatics. The fully coupled initial value problem is solved simultaneously by a finite difference approach. The model is validated by comparing calculated and measured resonant frequencies of various amorphous ribbons, which turned out to be in good agreement. When slightly adapting single material properties from the data sheet, the match is almost perfect. The model is then used to calculate the local magnetic and mechanical properties inside static and vibrating ribbons. These local distributions can be directly linked to the field dependence of the resonant frequency and its higher harmonics. [ABSTRACT FROM AUTHOR]

In this work we present a detailed study on the magnetostrictive contribution to Poisson ratio for samples under applied mechanical stress. Magnetic contributions to strain and Poisson ratio for cubic materials were derived by accounting elastic and magneto-elastic anisotropy contributions. We apply our theoretical results for a material of interest in magnetomechanics, namely, galfenol (Fe1-xGax). Our results show that there is a non-negligible magnetic contribution in the linear portion of the curve of stress versus strain. The rotation of the magnetization towards [110] crystallographic direction upon application of mechanical stress leads to an auxetic behavior, i.e., exhibiting Poisson ratio with negative values. This magnetic contribution to auxetic behavior provides a novel insight for the discussion of theoretical and experimental developments of materials that display unusual mechanical properties. [ABSTRACT FROM AUTHOR]

A frequency-tunable current sensor consisting of Terfenol-D/PZT/Terfenol-D magnetoelectric (ME) laminate and Fe73.5Cu1Nb3Si13.5B9 nanocrystalline alloy has been developed. Almost all ME current-sensing devices have higher outputs at resonance conditions, but this advantage is useful only for narrow bandwidth. For the purpose of broadband current sensing, a frequency up-conversion mechanism is introduced by means of nonlinearity of the field-dependence magnetostriction λ(H). Current sensitivity enhancement is realized by modulating the low-frequency dynamic magnetostrictive strain to its resonance conditions. This solution provides the possibility to achieve resonance-enhanced sensitivity at the power-line frequency of 50 Hz, and the capability to immune the noise floor. Experimental results show that the modulated sensitivity is increased from 48.6mV/A to 178.4mV/A at 50Hz, and a small current step change of 3mA can be clearly distinguished by amplitude or phase of the output signals. These results provide possibilities to accurately detect weak currents in the noise ambient at low frequencies. [ABSTRACT FROM AUTHOR]

A method for measuring the magnetostriction of thin films using a vibrating sample magnetometer is described. We describe the design of a custom sample holder to apply an adjustable bending stress to the sample during measurement and observe the resulting change in the M-H loop. [ABSTRACT FROM AUTHOR]

Three quasi-one-dimensional magnetoelectric (ME) magnetic field sensors, each with a different magnetostrictive wire material, were investigated in terms of sensitivity and noise floor. Magnetostrictive Galfenol, iron-cobalt-vanadium, and iron-nickel wires were examined. Sensitivity profiles, hysteresis effects, and noise floor measurements for both optimally biased and zero-biased conditions are presented. The FeNi wire (FN) exhibits high sensitivity (5.36 mV/Oe) at bias fields below 22 Oe and an optimal bias of 10 Oe, whereas FeGa wire (FG) exhibits higher sensitivity (6.89 mW/Oe) at bias fields >22 Oe. The sensor of FeCoV wire (FC) presents relatively low sensitivity (2.12 mV/Oe), due to low magnetostrictive coefficient. Each ME tube-topology sensor demonstrates relatively high sensitivity at zero bias field, which results from a magnetic shape anisotropy and internal strain of the thin magnetostrictive wire. [ABSTRACT FROM AUTHOR]

We have investigated a method for measuring the dimensions of an individual multilayered Fe- Ga/Cu nanowire (NW) as it changes with induced magnetization. In this study, we demonstrate the proposed approach and establish this as a viable method for measuring the magnetostrictive behavior of an individual Fe-Ga/Cu NW using atomic force microscopy (AFM). When an external magnetic field (~300 Oe) was applied perpendicular to the NW axis, the NW length appeared minimized. When a field (~1000 Oe) was applied parallel to the NW axis, the height profile of the NW was found to be higher than in the case with no parallel external field. Since both ends of the NW were welded to the substrate, the magnetic field induced dimensional change of the NW caused deflection of the NW in the upward direction, which was significant enough to be detected by AFM. An average height difference of 15nm was measured with and without an applied field which was then used to calculate the magnetostriction of the multilayered NW. [ABSTRACT FROM AUTHOR]

This paper analyzes a prototype microgyrosensor that employs the magnetostrictive alloy Galfenol for transduction of Coriolis-induced forces into an electrical output for quantifying a given angular velocity. The magnetic induction distribution in the Galfenol sensor patch depends on its bending shape and magnetoelastic properties and is investigated using a finite element model. Fluctuations in magnetic induction caused by a sinusoidal rotation of the sensor produce an amplitude modulated voltage in a surrounding coil which is simulated and measured. [ABSTRACT FROM AUTHOR]

Bulk ferromagnetic shape memory Fe68-Pd30-Rh2 and Fe66-Pd30-Rh4 (at. %) alloys were strain-forged to produce a 35%-40% reduction in thickness. The reduced alloys were thermally annealed at 950-1050 °C for various times to induce recrystallization. The magnetostriction test demonstrated that the grain size reduction of recrystallization had a direct influence on the magnetic properties of the materials. The magnetostrictive strain measurements revealed that the strain-forged metal treated with thermal recrystallization to induce the fine-grained structure had a higher magnetostriction as well as a higher magnetostrictive susceptibility (Δλ‖ s /Δ H). It was also found that at room temperature, the saturation magnetostriction (λs=77x10-6) of the fine-grained Fe- Pd-Rh alloys strain-forged with thermal recrystallization was higher than that of those without grain size reduction (λs=50-56x10-6), where λs is (2/3)[λ‖ s-λ⊥ s]. In addition, with the magnetic field applied perpendicular to the sample's longitude, the fine-grained Fe-Pd-Rh material contracted by as much as λ⊥ s=-36x10-6. This value is about three times higher than that of alloys without grain size reduction. Microstructure investigation indicated that a magnetic applied field normal to the sample's longitude caused high contraction (λ⊥ s) of the fine-grained Fe-Pd-Rh alloys, which could be ascribed mainly to the grain refinement as well as deformation twins or microtwins (transformation and transverse twins). The study demonstrates that the magnetostrictive strains of Fe-Pd-Rh alloys induced in the L10 martensite by the magnetic field can be attributed to the reorientation of the L10 martensite twin structures. [ABSTRACT FROM AUTHOR]

his paper investigates the origin of large magnetostriction in Fe-Ga alloys using small-angle neutron scattering (SANS) and Kerr microscopy. The SANS data for a single-crystal, electron irradiated, and quenched Fe81Ga19 sample under externally applied magnetic and elastic fields revealed the existence of magnetostrictive nanoclusters spaced at ∼15 nm apart that have a different magnetization than the A2 matrix. Combining the SANS results and the magnetization orientation obtained from the magnetic domain images using a Kerr microscope, it appears that the nanoclusters contribute significantly to the macroscopic magnetostriction. [ABSTRACT FROM AUTHOR]

CoFe2O4 (core)/BiFeO3 (shell) nanoparticles are prepared by varying the relative molar concentration of core and shell materials (40%CoFe2O4-60%BiFeO3, 50%CoFe2O4-50%BiFeO3, and 60%CoFe2O4-40%BiFeO3). The core-shell nature is confirmed from transmission electron microscopy on these samples. A plot of ΔM (=MFC-MZFC) vs temperature suggests the presence of two types of spin dynamics: (a) particle size dependent spin blocking and (b) spin-disorder. These two spin dynamic processes are found to contribute independently to the generation of magnetoelectric voltage. Very clear first order and second order magnetoelectric voltages are recorded. The resemblance of the first order magnetoelectric coefficient vs temperature plot to that of building up of order parameters in the mean field theory suggests that spin disorder can act like one of the essential ingredients in building the magnetoelectric coupling. The best result is obtained for the 50-50 composition sample, which may be due to better coupling of magnetostrictive CoFe2O4, and piezoelectric BiFeO3, because of the optimum thickness of shell and core. [ABSTRACT FROM AUTHOR]

Laminated amorphous FeSiBC films with various spacer layers, including Cu, Co0.45Cu0.55, Co0.8Cu0.2, and CoFe, were prepared in order to study the effect of interface structure and magnetic exchange interaction on the magnetic softness and uniaxial anisotropy of multilayered film. It is found that laminating FeSiBC film with thin nonmagnetic or weak magnetic spacers yields much lower coercivity and higher remanent magnetization than those with magnetic spacers. Optimal films with the desired properties of Hc ∼ 1.5 Oe, Mr/Ms = 95%, and Hk ∼ 16 Oe were obtained. Therefore, it is confirmed that the exchange interaction constant of spacer layer plays a more important role than that of interface structure. Furthermore, laminating FeSiBC with nonmagnetic layers only slightly changes magnetostrictive coefficient. [ABSTRACT FROM AUTHOR]

The paper deals with the mechanical vibrations damping effect induced by a magnetostrictive energy harvesting device properly working. The proposed experimental setup allows us to investigate, through time-domain measurements, the dependence of the mechanical damping from parameters like magnetic bias and external load, affecting the global harvested power. This result would underline the promising possibility to reduce mechanical vibrations and obtain power harvesting at the same time. [ABSTRACT FROM AUTHOR]

In this paper, we present the design and performance of a MEMS-device based on the magnetostrictive effect, which can be used as a micro-loudspeaker. The device basically consists of a comb structure of monomorph bending cantilevers with an active area up to 3.0×2.5 mm2. It produces a sound-pressure-level up to 101 dB at 400 Hz in a standard 2 ccm measurement volume. We show our measurement setup as well as a mechanic-acoustic-coupled lumped element model to calculate sound pressure. The model incorporates finite element results for mechanical behavior. Measurement results validate our model assumptions. [ABSTRACT FROM AUTHOR]