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Highlights • A non-hysteresis magnetization model for the GMA was presented using Arctangent function. • Proposed model is suitable to the condition when the maximum magnetization is higher than 20 kA/m. • Proposed model has similar effects to J-A model on computing the amplitude and change rule of the magnetization curve. • The model's accuracy on predicting the output displacement of GMA was verified using experimental data. Abstract Currently, most of the physics-based magnetization models for giant magnetostrictive actuator are complicated in their mathematical models. These complicated models pose considerable challenges for real-time control. Focus on the above issue, we proposed a fitting magnetization model using Arctangent function, as the inverse of the Arctangent function can solve it very quickly. This function was suitable to model the magnetic behavior of giant magnetostrictive actuator serving in an electronic controlled injector or other types of on-off valves. Applicable range of the model was determined through computing the maximum magnetic field. Then the deviations of the proposed fitting model and Jiles-Atherton model under different parameters were studied to verify the computing effects of the model. Then the effectiveness of the fitting model was verified by experimental results. With a high computing precision and a concise form, the proposed model shows great potentials for the real-time control of giant magnetostrictive actuators. [ABSTRACT FROM AUTHOR]

Highlights • Single-phase (Tb,Dy,Gd)(Co,Al) 2 alloys synthesized using high-purity metals. • Temperature dependence of lattice parameters measured in a wide temperature range. • The second order magnetostructural phase transitions like Curie temperatures (from cubic to the rhombohedral phase) are found. • The magnetostrictive properties and the MCE of the Tb 0.2 Dy 0.8−x Gd x Co 1.9 Al 0.1 (x = 0.3, 0.4, and 0.5) compounds were studied in detail. • The influence of partial substitution of Co by Al atoms on the magnetocaloric and magnetostrictive properties (Tb,Dy,Gd)Co 2. • Materials with 'table-like' MCE are found. Abstract The influence of partial substitution of Co by Al atoms on the magnetocaloric and magnetostrictive properties of the multicomponent Tb-Dy-Gd-Co compounds with a Laves phase structure was investigated. The samples were obtained by arc melting using of high-purity rare-earth metals. The crystal structure of Tb 0.2 Dy 0.8 - x Gd x Co 2 - y Al y (x = 0.3, 0.4, and 0.5; y = 0 and 0.1) compounds was monitored by powder X-ray diffraction. The magnetostriction and the magnetocaloric effect in external magnetic field up to 12 and 18 kOe, respectively, were studied in wide temperature range. The Curie temperature of Al-content compounds increases by an average of 20 K, while the magnitudes of the magnetocaloric effect and the magnetostriction slightly decrease. [ABSTRACT FROM AUTHOR]

Highlights • Effect on harvester performances of the magnetic bias correlated with preload. • Output power and voltage versus magnetic bias equations provided. • High output power obtained even with magnets having a relatively small coercive field. • Magnetic vs mechanical bias, at the maximum output power, depict a linear behavior. • Results validated with permanent magnets. Abstract The output power generated by a vibrational magnetostrictive energy harvester depends on several parameters, some of them linked to the mechanical source, as vibration amplitude and frequency, others related to design quantities, like mechanical preload, magnetic bias, coil turns and load impedance. Complex models have been developed in literature to reproduce the behavior of these devices. However, for output variables such as power and voltage, one moves in a space of many variables and it is not trivial to reconstruct an overall behavior of the device. The aim of this paper is to provide a wide picture concerning the device behavior investigating experimentally the output power and voltage as a function of the mechanical and especially magnetic bias, varying the amplitude and frequency of the driving vibration. A galfenol rod (Fe 81 Ga 19) sample inserted in a three-legged magnetizer is utilized to vary the magnetic bias and to provide the flux closure to the sample, while a dynamic test machine provides both the mechanical bias and the driving vibration at different frequencies up to 100 Hz. The paper analysis has highlighted that the output power and voltage depend on the magnetic bias according to an exponentially modified Gaussian distribution. Keeping constant the other parameters and varying the mechanical bias, a family of modified Gaussian distributions is obtained. Moreover, fixing the electric load, the amplitude and frequency of the vibration, the couple of values "magnetic bias – mechanical preload" corresponding to the maximum output power of the device depicts a linear behavior. The results here obtained point out that it is possible to simplify the design of magnetostrictive energy harvesters and to obtain high output power even with permanent magnets providing a relatively small coercive field. The results have been confirmed by using two yokes equipped with permanent magnets on the external columns. The maximum output average power obtained with permanent magnets has been 796 mW equal to 6.5 mW/cm3 with a sinusoidal vibration amplitude of 40 MPa at 100 Hz. [ABSTRACT FROM AUTHOR]

The rare-earth giant magnetostrictive material has received considerable attention in recent years and is known as a new type of high efficient magnetic – mechanical conversion material. Its performance is far superior to that of other materials such as piezoelectric ceramic and so on. Giant magnetostrictive actuator has been widely used in precise driving occasions for its excellent performance. The experimental analysis system for giant magnetostrictive material is designed. Several important parameters have been discussed separately by static and dynamic experiment. Further, the nonlinear magnetic hysteresis characteristic is analyzed by theoretical method. The turning machining analysis model is established and the analytical solution is verified by comparison with the test result. The influence of various parameters is discussed at the same time. Obviously, the research results and methods provide a basis for giant magnetostrictive actuator. [ABSTRACT FROM AUTHOR]

This paper discusses two different mechanisms of temperature effects on magnetoimpedance (MI), namely, the internal stress relaxation upon heating and critical behavior of magnetic parameters near the Curie temperature T c . When a microwire is heated, the residual stress is partially released changing the effective anisotropy, which inevitably leads to the temperature dependence of hysteresis and MI. A very large change in impedance up to 200% with moderate temperature increase (50–70 °C) occurs in microwires of Co 66.94 Fe 3.83 Ni 1.44 B 11.51 Si 14.59 Mo 1.69 compositions with high T c ≈ 340 ° C where the magnetostriction changes a sign from negative to positive due to stress relaxation. Proper annealing is demonstrated to stabilize such temperature variations in MI. Near the Curie temperature, the impedance undergoes large variations due to a corresponding drop in the magnetization saturation and magnetic anisotropy. The theoretical modelling reveals an increase in the dc initial permeability when approaching T c , which results in different temperature behaviours of MI at low and high frequencies. This was confirmed experimentally for Co 23.67 Fe 7.14 Ni 43.08 B 13.85 Si 12.26 amorphous microwires ( T c  = 62 °C): at a frequency of 10 MHz the impedance increases with temperature until very close proximity of T c , whilst at a frequency of 300 MHz it continuously decreases with increasing temperature. Controlling the value of T c the impedance temperature dependence can be realized in the industrial temperature range of 20–100 °C. This has potential applications for developing embedded miniature temperature sensors. [ABSTRACT FROM AUTHOR]

The Ga liquid and Al powder were mechanically mixed and poured into a hollow iron plate, after alloying, the composite plate was rolled at room temperature for preparing an Fe/Ga-Al composite strip. The effect of annealing conditions on the diffusion, microstructures and magnetostrictive properties of the strip were studied. The composite plate had good cold rolling formability. After annealing at 750–850 °C for 5 h of the cold-rolled sample with a reduction of 97%, the diffusion distance of Ga and Al in the Fe matrix increased with an increase of the annealing temperature. However, some holes appeared in the center of the sample annealed at a temperature of more than 830 °C, which was detrimental to the subsequent rolling. The combination of the secondary cold rolling and annealing was beneficial to improve the composition homogeneity and magnetic properties of the sample. The magnetostriction coefficient (λ // ) of the primary rolled sample was low, ∼4 × 10 −6 . After annealing and secondary cold rolling, the λ // of the sample increased to 9 × 10 −6 and the λ // of the sample conducted by further annealing at 820 °C for 20 h reached 27.5 × 10 −6 . [ABSTRACT FROM AUTHOR]

The intrinsic brittleness in giant magnetostrictive material TbDyFe alloy has devastating influence on the machinability and properties of the alloy, thus affecting its applications. The purpose of this paper is to study the mechanical properties of the TbDyFe alloy by alloying with Nb element. The samples (Tb 0.3 Dy 0.7 ) x Fe 2x Nb y (y = 0, 0.01, 0.04, 0.07, 0.1; 3x + y = 1) were melted in an arc melting furnace under high purity argon atmosphere. The microstructure, magnetostrictive properties and mechanical performance of the alloys were studied systematically. The results showed that NbFe 2 phases were observed in the alloys with the addition of Nb. Moreover, both the NbFe 2 phases and rare earth (RE)-rich phases were increased with the increasing of Nb element. The mechanical properties results revealed that the fracture toughness of the alloy with the addition of Nb enhanced 1.5–5 times of the Nb-free alloy. Both the NbFe 2 phase and the RE-rich phase had the ability to prevent crack propagation, so that they can strengthen the REFe 2 body. However, NbFe 2 phase is a paramagnetic phase, which can reduce the magnetostrictive properties of the alloy by excessive precipitation. [ABSTRACT FROM AUTHOR]

This study develops a rate-dependent constitutive model which includes pinning site loss and eddy current loss for magnetostrictive materials. The static pinning site loss is described by an energy-weighted averaging framework; the stress- and field-induced eddy current loss is defined by Maxwell’s equations. Due to the eddy currents, the magnetic field in magnetostrictive materials is inhomogeneous especially when the excitation frequency is beyond the cut-off frequency. The model developed in this study is able to capture the stress- and field-induced magnetic diffusion. Analytical solutions are derived for magnetostrictive rods and minor loop responses. However, numerical solutions can be found for other geometries and large input amplitudes using the same modeling algorithm. The model is used to interpret flux density versus stress measurements of a highly-textured, 〈 1 0 0 〉 -oriented, polycrystalline Fe 81.6 Ga 18.4 rod under constant current biasing. The model accurately and efficiently reproduces the nonlinear magnetostrictive behavior up to 800 Hz, which is much higher than the cut-off frequency. [ABSTRACT FROM AUTHOR]

Based on the thermodynamic theory, by introducing the Weiss molecular field and considering current eddy loss, a 1D nonlinear elasto-thermo-magnetic multi-field coupling hysteresis constitutive model is proposed for giant magnetostrictive materials. This new model can fully describe the effects of the stress, frequency and ambient temperature not only on the curves of magnetostriction and magnetization under the static frequency, but also on the hysteresis characteristics of magnetostriction and magnetization at the dynamic frequency. This model, which has more concise mathematical form compared with other related models, shows a good agreement with experimental results on the magnetostrictive strain and magnetization hysteresis loops. Furthermore, the predicted results have indicated the necessary of considering the Weiss molecular field. This model is of convenient for both theoretical researches and engineering applications of magnetostrictive materials due to being without piecewise function and implicit functions in magnetostrictive constitutive relations. [ABSTRACT FROM AUTHOR]

In this work, amorphous FeSiB and FeGaSiB thin films have been fabricated on silicon substrates using a co-sputtering-evaporation deposition technique. The effect of adding gallium into FeSiB (Metglas) thin films on the structure, magnetic properties and magnetostriction have been studied. From X-ray diffraction (XRD), all the films were amorphous and the observed peaks were for the Si substrate. X-ray Photoelectron Spectroscopy (XPS) measurements were carried out to determine the film’s composition, which was found to be Fe 83 Ga 11 Si 5.2 B 0.8 . Atomic force microscopy (AFM) images were taken to measure the film thickness along with studying the surface topography. It was found that the film surface had an average roughness of 0.461 nm. For both FeSiB and FeGaSiB thin films, the effect of the thickness of the films on the magnetic properties and magnetostriction were investigated. The results showed that adding Ga into the FeSiB films changed the magnetic properties by reducing the saturation induction along with changing the magnetic anisotropy from uniaxial to isotropic. For the FeGaSiB films, the coercive field decreased and the saturation field (H s ) increased with film thickness. The magnetostriction constants of the FeGaSiB films were all larger than the FeSiB films for thicknesses greater than 40 nm. [ABSTRACT FROM AUTHOR]

Since their birth or mergence the late 1980s, the nanocrystalline ultrasoft magnetic materials are taking a great importance in power electronic systems conception. One of the main advantages that make them more attractive nowadays is their ability to be packaged since the reduction of the magnetostrictive constant to almost zero. In aircraft applications, due to the high component compactness and to their location (for example near the jet engine), the operating temperature increases and may reach easily 200 °C and more. Consequently, the magnetic thermal ageing may occur but is, unfortunately, weakly studied. This paper focuses on the influence of the coating (packaging type) on the magnetic nanocrystalline performances during a thermal ageing. This study is based on monitoring the magnetic characteristics of two types of nanocrystalline cores (naked and coated) during a thermal activated ageing (100, 150 and 200 °C). Based on a dedicated monitoring protocol, a large magnetic characterization has been done and analyzed. Elsewhere, X-Ray Diffraction and magnetostriction measurements were carried out to support the study of the anisotropy energies evolution with ageing. This latter is discussed in this paper to explain and give hypothesis about the ageing phenomena. [ABSTRACT FROM AUTHOR]

Magnetostrictive Cu 0.1 Co 0.9 RE x Fe 2- x O 4 (RE=Ho, Gd or Sm) was fabricated by a sol-gel auto-combustion technique using spent lithium-ion batteries as raw materials. X-ray diffraction analysis confirmed the spinel structure of the RE-incorporated samples with limited RE solubility. Field-emission scanning electron microscopy and Fourier transform infrared spectroscopy revealed a layered structure composed of particles and the cation distribution. Magnetic hysteresis loops and magnetostriction strain curves showed that the saturation magnetization, magnetostriction coefficient and strain derivative were significantly modified due to the substitution of larger ionic radius RE 3+ ions for Fe 3+ ions, influencing the interaction between the tetrahedral and octahedral sites. [ABSTRACT FROM AUTHOR]

For glass-coated amorphous ferromagnetic Fe-based microwires both joint and separate effect of metallic nucleus diameter, d , and the ratio of metallic nucleus diameter to the total diameter of microwire in glass shell, d/D , on magnetic properties is investigated. Thereby the contribution of both shell-induced stresses, associated with the ratio of diameters, and internal nucleus stresses (residual, quenching), associated with the diameter of the nucleus are estimated. A strong and non-monotonic effect of the metallic nucleus diameter and metallic nucleus diameter/total microwire diameter ratio on magnetostatic and magnetostrictive properties was established. For analysis, we considered magnetically bi-stable microwires of “classic” Fe 77.5 Si 7.5 B 15 alloy with positive magnetostriction coefficient. [ABSTRACT FROM AUTHOR]

Giant magnetostrictive actuator has been widely used in precise driving occasions for its excellent performance. However, in driving a switching valve, especially the ball-valve in an electronic controlled injector, the actuator can’t exhibit its good performance for limits in output displacement and responding speed. A novel giant magnetostrictive actuator, which can reach its maximum displacement for being exerted with no bias magnetic field, is designed in this paper. Simultaneously, elongating of the giant magetostrictive material is converted to shortening of the actuator's axial dimension with the help of an output rod in “T” type. Furthermore, to save responding time, the driving voltage with high opening voltage while low holding voltage is designed. Responding time and output displacement are studied experimentally with the help of a measuring system. From measured results, designed driving voltage can improve the responding speed of actuator displacement quite effectively. And, giant magnetostrictive actuator can output various steady-state displacements to reach more driving effects. [ABSTRACT FROM AUTHOR]

• This paper presents the implementation of magneto-mechanical constitutive law utilizing thermodynamic approach in a 3D finite element solver using COMSOL Multiphysics software. • The approach is successfully validated against measurements from a cantilever beam type harvester. • Effect of magnetostriction over resonant frequency is investigated. • The model fits well to the magnetization curves measured under static loading. • The model is validated with the measurements results following the trends reasonably. This paper presents the validation of a thermodynamic magneto-mechanical model to analyze a galfenol based cantilever beam type energy harvesting device. As compared to some earlier modeling approaches that were tested only on specific harvester geometries, the thermodynamic model has already been validated on rod-type harvesters and is now shown to be suitable for analyzing also beam-type devices. Moreover, the paper discusses the influence of magnetostriction upon resonant frequency. The thermodynamic model is implemented in a 3D finite element solver using COMSOL Multiphysics software. This allows optimizing the device design by tuning the geometric parameters and magnetic bias under available operating conditions (amplitude and frequency of vibrations) easily and efficiently. A unimorph cantilever beam type prototype harvester device consisting of a galfenol beam bonded to an aluminum substrate is constructed for validating the model. Simulated and measured results are compared at base excitation amplitudes of 0.5 to 2 g under varying vibration frequencies. The results show that the maximum induced voltage is obtained at the resonant frequency which decreases slightly with an increase in the vibration amplitude. Furthermore, it is shown that the resonant frequency decreases from 201 Hz to 187 Hz at 1 g base acceleration when the magnetic bias is removed. The comparison of measured and simulated results show that the model can accurately predict the resonant frequency with a relative error of less than 2 %, validating the modeling approach. The model can also reasonably determine the open circuit voltage with some discrepancies at large vibration amplitudes. [ABSTRACT FROM AUTHOR]

In present work we have investigated magnetostrictive ultrasound generation by spiral magnets in the vicinity of magnetic field induced phase transition from spiral to collinear state. We found that such magnets may generate transverse sound waves with the wavelength equal to the spiral period. We have examined two types of spiral magnetic structures: with inhomogeneous exchange and Dzyaloshinskii–Moriya interactions. Frequency of the waves from exchange-caused spiral magnetic structure may reach some THz, while in case of Dzyaloshinskii–Moriya interaction-caused spiral it may reach some GHz. These waves will be emitted like a sound pulses. Amplitude of the waves is strictly depends on the phase transition speed. Some aspects of microwaves to hypersound transformation by spiral magnets in the vicinity of phase transition have been investigated as well. Results of the work may be interesting for investigation of phase transition kinetics as well, as for various hypersound applications. [ABSTRACT FROM AUTHOR]

In this paper both linear and nonlinear magnetoelectric (ME) effects have been investigated intensively. In order to obtain magnetic amplification, we fabricated 3 multi-push–pull mode magnetoelectric laminated composites metglas/PMNT/metglas based on dumbbell-shaped metglas. The linear magnetoelectric charge coefficient is enhanced to 2600 pC/Oe at 2 Hz based on dumbbell-shaped metglas and it increases as the end-flange width of the dumbbell-shaped metglas increases at 2 Hz, respectively. Based on these 3 ME composites, we establish an active mode nonlinear modulation system for ME magnetic sensor, the sensitivity of which are enhanced to 80, 100 and 102 pT / √ Hz at 1 Hz for the composites with the end-flange width 20, 15 and 10 mm, respectively, via nonlinear ME　modulation method. Strain distribution simulations illustrate the theoretically accurate amplification of the dumbbell-shaped geometry. The center strains of 3 dumbbell-shaped metglas decrease as the width of end-flanges decreases [ABSTRACT FROM AUTHOR]

The main aim of the work was to show the correlation between magnetostrictive properties and microstructure of 25 nm thick Co 90 Fe 10 films deposited on soft magnetic underlayers. A special attention was paid to the role of the interface region. In the case of Co 90 Fe 10 on 25 nm and 35 nm thick METGLAS underlayers one can resolve in conversion electron Mössbauer spectra two hyperfine field distributions (high-field and medium-field ones) corresponding to both constituents of bilayers. Analogical distributions describe the spectra of Co 90 Fe 10 on 25 nm and 35 nm thick Ni 81 Fe 19 underlayers, however an additional low-field, smeared component has been observed. It has been attributed to the interface layer (of partially disordered structure) between magnetostrictive layer and soft magnetic layer. Such interpretation is backed up by the obtained strong correlation between mean hyperfine field value and magnetostriction constant of the films. The investigated bilayers are good candidates for MRAM devices. [ABSTRACT FROM AUTHOR]

Oriented polycrystalline CoFe 2 O 4 have been prepared via a ceramic method. The CoFe 2 O 4 powder was mixed with polyvinyl alcohol solution to produce semisolid slurries. The slurries were oriented under a magnetic field of 2 T, and were then sintered at 1623 K. The maximum magnetostriction λ s up to −270×10 −6 and strain derivative ( dλ / dH ) max of 7.7×10 −9 m/A were achieved for oriented samples. Results show that a preferred <001> orientation has been obtained within oriented sample. [ABSTRACT FROM AUTHOR]

Tunnel magnetoresistance (TMR) junctions with CoFeB/MgO/CoFeB layers are promising for strain sensing applications due to their high TMR effect and magnetostrictive sense layer (CoFeB). TMR junctions available even in submicron dimensions can serve as strain sensors for microelectromechanical systems devices. Upon stress application, the magnetization configuration of such junctions changes due to the inverse magnetostriction effect resulting in strain-sensitive tunnel resistance. Here, strain sensitivity of round-shaped junctions with diameters of 11.3 μm, 19.2 μm, 30.5 μm, and 41.8 μm were investigated on macroscopic cantilevers using a four-point bending apparatus. This investigation mainly focuses on changes in hard-axis TMR loops caused by the stress-induced anisotropy. A macrospin model is proposed, supported by micromagnetic simulations, which describes the complete rotation of the sense layer magnetization within TMR loops of junctions, exposed to high stress. Below 0.2‰ tensile strain, a representative junction with 30.5 μm diameter exhibits a very large gauge factor of 2150. For such high gauge factor a bias field H = - 3.2 kA / m is applied in an angle equal to 3 π / 2 toward the pinned magnetization of the reference layer. The strain sensitivity strongly depends on the bias field. Applying stress along π / 4 against the induced magnetocrystalline anisotropy, both compressive and tensile strain can be identified by a unique sensor. More importantly, a configuration with a gauge factor of 400 at zero bias field is developed which results in a straightforward and compact measuring setup. [ABSTRACT FROM AUTHOR]

The influence of annealing process, including heating rate and final annealing atmosphere, on texture evolution and magnetostrictive performance of rolled 0.16wt% NbC doped Fe–Ga sheets has been investigated. It demonstrates that texture evolution is closely related with heating rate, and strong Goss texture {110}〈001〉 was obtained at 0.25°C/min after the heating process from 900°C to 1080°C, accompanied with a peak value of saturation magnetostriction. Non-Goss texture and deviation from ideal {110}〈001〉 were observed at lower or higher heating rate, resulting in the decrease in saturation magnetostriction. Compared with pure-Ar annealed sheets, the hydrogen introduced into annealing atmosphere during final treatment promoted (110) grain growth and eliminated the Nb-rich precipitates, and additional improvement in the saturation magnetostriction was observed for the same annealing protocols, with a maximum measured value, (3/2)λs=λ //−λ ⊥ , of 233×10−6 obtained in the final Ar/H2 annealed sheet. [ABSTRACT FROM AUTHOR]

Abstract: The influence of torsional stress on the asymmetric magnetoimpedance in a glass-coated negative magnetostrictive amorphous microwire due to bias current is studied theoretically. The longitudinal and off-diagonal impedance components are found assuming a simplified spatial distribution of the magnetoelastic anisotropy induced by the torsional stress. The asymmetry in the field dependence of the impedance components is attributed to the combination of the circular magnetic field produced by the bias current and a helical anisotropy induced by the torsional stress. The asymmetry in the magnetoimpedance and the low-field hysteresis are analyzed as a function of the bias current and torsional stress. It is shown that the application of torsional stress significantly changes the value of the bias current required to suppress the hysteresis effect. The results obtained may be useful for applications in magnetic-field and stress sensors. [Copyright &y& Elsevier]

Abstract: Magnetoelectric effect in multiferroic materials is widely studied for its fundamental interest and practical applications. The magnetoelectric effect observed for single phase multiferroics is usually small. A much larger effect can be obtained in composites consisting of magnetostrictive and ferroelectric phases. This paper investigates the magnetoelectric effect of multilayer (laminated) structure consisting of 7 nickel ferrite and 8 PFN relaxor layers. It describes the synthesis and tape casting process for Ni0.3Zn0.62Cu0.08Fe2O4 ferrite and relaxor PbFe0.5Nb0.5O3 (PFN). Magnetic susceptibility, hysteresis, ZFC–FC curves and dependencies of magnetization versus temperature for PFN relaxor and magnetoelectric composite were measured with a vibrating sample magnetometer (VSM) in an applied magnetic field up to 85kOe at a temperature range of 10–400K. Parallel and perpendicular magnetostriction of the pure ferrite and bulk and laminated composites were measured at room temperature as a function of the magnetic field (0.3–6.5kOe). Magnetoelectric effect at room temperature was investigated as a function of the static magnetic field (0.3–6.5kOe) and the frequency of the sinusoidal magnetic field (0.01–6.5kHz). At lower magnetic field, the magnetoelectric coefficient increases slightly before reaching a maximum and then decreases. The magnetoelectric coefficient α ME increases continuously as the frequency is raised, although this increase is less pronounced in the 1–6.5kHz range. The maximum values of magnetoelectric coefficient attained for the layered composites exceed about 50mV/(Oecm). [Copyright &y& Elsevier]

• NdFeB thin films developed by pulsed laser deposition onto Si substrates. • Five single alloy targets with different atomic compositions tested and studied. • 150 nm thin films @ 600 °C present very good hard magnetic properties. • Single magnetic phase, both coercivity and remanence above 1 T, a square loop shape. • Magnetic properties ascribed to film texturation and to partial magnetic decoupling. Nd-Fe-B thin films have been successfully developed by Pulsed Laser Deposition (PLD) onto silicon substrates. In order to explore the crucial role of target composition during PLD, five single alloy targets, representing specific atomic compositions (Nd/Fe atomic ratio varied in the range 0.18–0.47) have been tested and studied. In a determined deposition temperature range of 550 °C-630 °C, thin films made from a target with Nd/Fe = 0.45 present the best hard magnetic properties, a quasi-single magnetic phase, both coercivity and remanence above 1 T and a square loop shape. FIB-ESB analyses associated with XRD, SEM and SQUID-VSM magnetic measurements indicate that the high values of both remanent magnetization and coercivity are ascribed to film texturation and to partial decoupling of the hard magnetic Nd 2 Fe 14 B grains by a secondary Nd-rich phase. PLD performed with other target compositions and non-optimized deposition temperatures leads to poorer magnetic properties, owing to the presence of soft magnetic phase and non-textured or oxidized thin films. [ABSTRACT FROM AUTHOR]

• It allows 3D analysis of an energy harvester device efficiently and accurately. • Provides simplified approach, serves as a design tool for magnetostrictive harvesters. • Effect of design parameters and operating conditions on harvester performance. • The model fits well to the magnetization curves measured under static loading. • The model is validated with the measurements results following the trends reasonably. This paper presents the implementation of magneto-mechanical constitutive law utilizing thermodynamic approach in a 3D finite element solver using COMSOL Multiphysics software. The analytical expression for the magnetic field strength and stress is derived from the constitutive model utilizing magnetic flux density and mechanical strain as state variables. The constitutive model is successfully implemented in commercially available software COMSOL. This implementation allows 3D analysis of an energy harvester device efficiently and accurately. A prototype concept device is developed to validate the model and its implementation. The device is tested under uniaxial compressive loading by varying the preload, dynamic load and magnetic bias. The model is validated by comparing the simulated and experimental results. The comparison shows that the model can reasonably predict the optimal value of the preload and magnetic bias yielding maximum power and is able to follow the measurement trends. This model can be used as a suitable tool to analyze the behavior of the concept energy harvesters and determine the optimal design parameters. [ABSTRACT FROM AUTHOR]

• High-quality Galfenol thin films have been fabricated on MgO substrate by Sputter Beam Epitaxy. • FMR spectroscopy demonstrates low effective damping parameter and narrow linewidth. • Magnetometry and FMR reveals low coercivity as well as expected in-plane anisotropy. • Galfenol thin films may be a promising candidate for low loss microwave devices. Fabrication of voltage tunable high-frequency devices using magnetostrictive ferromagnet-piezoelectric hybrid structures requires materials with low damping and narrow linewidth to achieve low microwave loss. Galfenol exhibits superior magnetostriction, stability over a wide range of temperatures, and is free of rare earth elements, making it an economical and promising candidate, if the microwave losses can be minimized. We report the fabrication, structural and magnetic characterization, and study of dynamic properties of epitaxial FeGa thin films exhibiting an ultra-low residual linewidth, Δ H 0 = 13 ± 1 Oe – a requirement for low microwave loss and effective damping parameter, α eff , as low as 0.0065 - 0.0001 + 0.0005 for the 16 nm thick film. Similarly, we found α eff = 0.0039 - 0.0007 + 0.0028 and Δ H 0 = 71 ± 1 Oe for the 24 nm thick film, demonstrating its potential for applications in magnetic memory and high frequency devices. [ABSTRACT FROM AUTHOR]