Low Magnetostriction Research Articles

Effect of annealing conditions on giant magnetoimpedance of Co-rich glass-coated microwires

In this article we study the effect of conventional and stress annealing on the magnetic properties and giant magnetoimpedance (GMI) effect of Co65.3Si12.0B10.2Cr8.5Fe3.9Mo0.1 microwires with low and positive magnetostriction coefficient and low Curie temperature. A remarkable tuning capacity of both GMI effect and hysteresis loops is observed for a broad range of annealing conditions up to 350∘C and 320 MPa. We report appearance of double-peaks magnetic field dependencies of the GMI-ratio related with the coexistence of two different contributions originated by two different magnetic domain structure for the stress-annealed microwires. The observed experimental results are discussed in terms of the internal stresses relaxation derived from the annealing procedures, the induced magnetic anisotropy and local atomic reordering. The studies of Co-rich microwires with low and positive magnetostriction coefficient and low Curie temperature are potentially suitable for development of smart composites with embedded microwires for wireless temperature monitoring.

A two-step stress-annealing with stress-relaxation process for developing low-loss Fe-based nanocrystalline soft magnetic cores

Fe72.5Nb2Mo2Cu1Si15.5B7 at.% nanocrystalline soft magnetic ribbon was stress-annealed at several temperatures around its primary crystallization temperature and magnetic properties were characterized in strips to determine conditions that led to minimal magnetic coercivity, Hc. This optimal stress-annealing (SA) temperature, though yielding minimal Hc in strips, also produced non-linear or rounded BH loops in wound cores. The rounded loops could be changed to linear or flat B-H loops following a secondary static annealing process. Through X-ray diffraction, transmission electron microscopy, and indirect magnetostriction measurements, we determined that the change in loop shape was driven by additional crystallization and stress-relief from the static annealing process. A change in mechanical properties including fracture toughness, loss modulus, and Young’s modulus after SA, were shown to limit the processability of the ribbon. Tape-wound inductors subjected to the optimal 640 °C / 85 MPa / 4 s SA process followed by a static annealing treatment of 500 °C for 1 h resulted in flat loops, an Hc of 0.3 A/m, low magnetostriction of ∼ 2 ppm, and core losses of only 7 W/kg at an induction of 0.4 T when excited at 20 kHz.

Interplay between D019, L12 and D03 phases in Fe3Ga-type alloy

Analysis of the first-order transition between D03 and two close-packed phases (L12, D019) in Fe3Ga-type alloy (26.9 %Ga), is carried out at different cooling rates from the range of equilibrium D019 phase and at different cooling rates from the range of equilibrium A2 phase. The structure was controlled by neutron diffraction, SEM-EBSD and additionally characterized using VSM and ATP tests. The obtained results clarify kinetics of D019 phase growth and transition to low temperature equilibrium L12 phase. We demonstrated that D019 phase is ferromagnetic at room temperature with very low saturation magnetostriction.

Electrodeposited NiFeCo + Tb and Dy for enhanced magnetostrictive properties and soft magnetism

Magnetostrictive thin films have numerous applications in communications, sensors, and microelectronic devices. Such devices usually require magnetostrictive thin films with large magnetostriction and soft magnetic properties. Nickel-Iron-Cobalt (NiFeCo) alloys have excellent soft magnetic properties and can be easily fabricated as thin films. However, their main drawback for these sensing applications is that they have very low magnetostriction. On the other hand, Iron-Rare Earth (RE) alloys such as Fe-Tb-Dy or Fe-Ga have large magnetostriction at the cost of some soft magnetic properties. Moreover, their magnetostrictive properties are degraded when reduced to thin films as opposed to bulk materials due to structural imperfections and oxidation of the REs. In this paper, we report the development of NiFeCo thin films with incorporated rare earth elements prepared via electrodeposition. Electrochemical cells were prepared using Ni, Fe, and Co sulfate salts. Tb and Dy sulfates were added to the electrochemical cell in order of increasing concentration. Electrodeposition was then carried out under galvanostatic control for each RE concentration in the bath. The produced films were analyzed for composition, crystallinity, and magnetic properties to draw out trends based on the initial concentrations of rare earth salts in the bath. The produced thin films retained soft magnetic properties while exhibiting giant magnetostriction of up to ∼370 ppm depending on the type and amount of incorporated REs within the film. The combination of soft magnetism and giant magnetostriction makes these NiFeCo thin films with added Tb and Dy excellent candidates for developing resonant frequency sensing devices.

Extremely low coercivity of powder Co-rich amorphous alloy obtained by gas atomisation

A novel Co-base soft magnetic powder with ultra-low coercivity was produced by inert gas atomisation. The as-atomised powder is fully amorphous owing to its high glass forming ability and the proper selection of atomisation conditions; it exhibits a very low coercivity (0.130 Oe) mainly due to the low magnetostriction coefficient of Co-based alloys. After production, the powder was annealed at different temperatures between 300 and 600 ºC for 30 minutes. Crystallisation started at around 575 ºC, which is the temperature of the first exothermic peak detected by differential scanning calorimetry. Annealing the powder at temperatures below 550 ºC develops only structural relaxation of the amorphous structure. The smallest coercivity (0.056 Oe) was found in the sample annealed at 400 ºC. On the other hand, an increment of the coercivity of four orders of magnitude occurred after full crystallisation at 600 ºC (394.320 Oe). From the analysis of the curves of anisotropy field distribution, it can be concluded that this Co-base alloy shows lower average anisotropy field, a more gaussian shape and a wider distribution than Fe-base alloys. This is explained by a lower magnetoelastic anisotropy and a more homogeneous distribution of the magnetic anisotropy. The powder exhibits a spherical shape that makes it very suitable as ferromagnetic phase to manufacture powder cores with extremely low hysteresis loss for medium-high frequency applications.

Formulation of energy loss due to magnetostriction to design ultraefficient soft magnets

The mechanism of energy loss due to magnetostriction in soft magnetic materials was analytically formulated, and our experiments validated this formulation. The viscosity of magnetic materials causes the resistive force acting on magnetic domain walls through strain due to magnetostriction, and magnetic energy is eventually dissipated by friction even without eddy currents. This energy loss mechanism explains the frequency dependence of the excess loss observed in the experiments, and the excess loss is dominated by the contribution of magnetostriction when the magnetostriction constant exceeds approximately 20 ppm. The random anisotropy model was extended by considering the effect of local magnetostriction as a correction to the magnetocrystalline anisotropy. The effect of magnetostriction was considerably suppressed by the exchange-averaging effect. The estimated effective random magnetoelastic anisotropy for nanocrystalline α-Fe reached as low as 18.6 J/m3, but this static effect could not explain the high excess loss at high frequencies observed in the experiments. The results of this research could provide new design criteria for high-performance soft magnetic materials based on low magnetostriction to reduce the excess loss.

The Magnetostriction of Amorphous Magnetic Microwires: The Role of the Local Atomic Environment and Internal Stresses Relaxation

We studied the magnetostriction coefficients, λs, Curie temperature, Tc, and their dependence on annealing conditions in Fe47Ni27Si11B13C2 and Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 amorphous glass-coated microwires with rather different character of hysteresis loops. A positive λs ≈ 20 × 10−6 is observed in as-prepared Fe47Ni27Si11B13C2, while low and negative λs ≈ −0.3 × 10−6 is obtained for Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 microwire. Annealing affects the magnetostriction coefficients and Curie temperatures, Tc, of both Fe47Ni27Si11B13C2 and Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 glass-coated microwires in a similar way. Observed dependencies of hysteresis loops, λs and Tc on annealing conditions are discussed in terms of superposition of internal stresses relaxation and structural relaxation of studied microwires. We observed linear λs dependence on applied stress, σ, in both studied microwires. A decrease in the magnetostriction coefficient upon applied stress is observed for Co-rich microwires with low and negative magnetostriction coefficient. On the contrary, for Fe-Ni-rich microwires with a positive magnetostriction coefficient, an increase in the magnetostriction coefficient with applied stress is observed. The observed results are discussed considering the internal stresses relaxation and short range atomic rearrangements induced by annealing on hysteresis loops, magnetostriction coefficients and Curie temperatures of studied microwires.

Radial Electromagnetic Force Estimation Using Strain Gauges in Switched Reluctance Motors

This study proposes a novel estimation method of the radial electromagnetic force in airgaps using strain gauges attached to the stator teeth in switched reluctance motors (SRMs). The proposed method compensates for the errors owing to magnetostriction and the non-uniform strain distribution on stator teeth. To verify the method, two test SRMs are fabricated with two different core materials; the 6.5% high silicon steel (10JNEX900) and amorphous iron (2605SA1), which have significantly different magnetostriction characteristics. Without the proposed compensations, the estimated radial force is higher than the finite element analysis (FEA) results owing to the extra deformation caused by magnetostriction. After applying the proposed method, the estimated force has good correspondence with the FEA results, and the error is reduced from 24% to 4% in the high silicon steel SRM. Regarding the amorphous iron SRM, the force estimated error was as high as 413% without compensations and is reduced to 64% by the proposed method. Additionally, the force waveforms are deformed because of the subtraction of the dominant magnetostrictive strain and phase delay in the amorphous iron SRM. In conclusion, the proposed method is effective in estimating the radial force on core materials with low magnetostriction.

Effect of temperature on magnetoimpedance in amorphous microconducts Co-=SUB=-27.4-=/SUB=-Fe-=SUB=-5-=/SUB=-Ni-=SUB=-43.08-=/SUB=-B-=SUB=-12.26-=/SUB=-Si-=SUB=-12.26-=/SUB=-

A study of the temperature behavior of high-frequency magnetoimpedance (MI) in amorphous microcircuits in a glass shell up to the Curie temperature TC has been carried out. Samples from the alloy Co27.4Fe5B12.26Si12.26Ni43.08 with a low Curie temperature (TC~48oC) and negative magnetostriction were used. Near TC, the impedance curves retain their characteristic behavior for materials with circular anisotropy, but the sensitivity of MI with respect to the field decreases sharply. The change in impedance with temperature becomes significant only in the presence of an external magnetic field. With an increase in temperature from room temperature to TC, the relative change in impedance can reach 140-275% in the frequency range 0.1-0.9 GHz and a magnetic field of ~10 Oe. Taking into account the location of TC in an almost important temperature region, the results obtained are interesting for the development of miniature temperature sensors, including contactless embedded sensors. Keywords: amorphous alloys, MI-effect, circular anisotropy, spin-orientation transition.

Structure, magnetostriction and elastic properties of an Fe3Ga0.7Cu0.3 alloy

• Presence of Ga in α-Fe lattice significantly expands limit of Cu solubility in it. • Alloy FeGaCu contrary ab initio -based predictions has low magnetostriction . • The reason is 25% increase in modulus of elasticity compared to classic FeGa. Within the framework of the theory of the influence of the electronic structure on the magnetostriction in FeGa alloys, it is believed that the addition of copper to a binary alloy can lead to an increase in its magnetostriction. In this work, experimental studies of an Fe 3 Ga 0.7 Cu 0.3 composition were carried out, which revealed that copper alloying led to a significant increase of the elastic modulus resulting in the degradation of magnetostriction.

Inverse Magnetostrictive Effect in Ni<SUB>x</SUB>Fe<SUB>1-x</SUB> (1≤ x ≤0.8) Thin Films Deposited on a Polypropylene Substrate

The magnetostriction effect is a unique phenomenon observed in magnetic materials due to applied stress. The permeability μ of the magnetic material increases or decreases depending on the sign of the magnetostriction coefficient λ based on the direction of the applied stress. For example, nickel has a negative λ, whereas iron has a positive λ for the same tensile (+) or compressive (-) stresses. However, the magnetostriction effect is reported to disturb the functionality of some spintronic applications, such as magnetic sensors and actuators, under the influence of an external magnetic field. Therefore, suppression of the magnetostriction effect is a challenge in developing flexible spintronic devices. In this study, the magnetostriction effect of the NiSUBx/SUBFeSUB1-x/SUB thin films was investigated under different stress conditions. The composition of the thin film was manipulated by varying the deposition thickness of nickel and NiSUB8/SUBFe₂ targets using a co-sputtering system. Magnetization reversal behaviors of the NiSUBx/SUBFeSUB1-x/SUB thin films were observed under the influence of an external magnetic field by using a vibrating sample magnetometer (VSM), before and after the application of bending stress. The negative magnetostriction effect of nickel was decreased by increasing the iron composition in the thin film, owing to the opposite sign of the magnetostriction coefficient. Finally, an extremely low magnetostriction was achieved at x = 0.8. The results of this study suggest that the magnetostriction effect can be controlled by varying the composition of the thin films and a sufficiently small magnetostriction effect can be observed at the permalloy composition between nickel and iron.

Advances in Fe-based amorphous/nanocrystalline alloys

Fe-based amorphous/nanocrystalline alloys exhibit excellent soft magnetic properties, including high saturation magnetic flux density (Bs), high permeability, low coercivity (Hc), and low magnetostriction. They are utilized in distribution transformers, transformers, reactors, and other devices. As green, energy-saving, and environmentally friendly materials, their application fields have more possibilities. In this paper, the development history, composition design principle, heat treatment process, magnetic properties, and annealing brittleness of Fe-based amorphous/nanocrystalline alloys are introduced.

Magnetic-field-tuned valence susceptibility in CeCo1−x Fe x Si revealed by magnetostriction

We report magnetoelastic studies in the CeCo1−x Fe x Si alloys. Iron doping has a profound effect on the low temperature linear magnetostriction. At T = 2 K, the strength of the magnetostriction peaks at x = 0.23 where it reaches a value as large as in an applied magnetic field B = 16 T. This Fe concentration corresponds to the critical one xc above which long-range antiferromagnetic order is no longer observed. The progressive increment of the hibridization between the Ce 4f orbital and the conduction band, as the magnetic order vanishes, gives rise to a sizeable valence susceptibility that can be finely tuned by the magnetic field explaining the large magnetostrictive effect around xc . At higher x, the magnetostriction decreases, in agreement with a weaker valence susceptibility resulting from a stronger hibridization.

Comment on "Ultralow magnetostrictive flexible ferromagnetic nanowires" by G. Muscas, P. E. Jönsson, I. G. Serrano, Ö. Vallin, and M. V. Kamalakar, Nanoscale, 2021, 13, 6043-6052.

In a recent paper (G. Muscas et al.),1 the magnetomechanical behavior of cobalt (Co) magnetic nanowire arrays on a polymeric substrate (polyethylene naphthalate (PEN)) under bending was measured by magneto-optical Kerr effect (MOKE) magnetometry in situ. The authors showed that the magnetomechanical effects were very small and assigned this result to a low effective magnetostriction coefficient due to the nanostructuring. In this comment, we show by numerical calculations that it is the ongoing/current stress distribution within the system that generates this effect. Indeed, the nanostructures being very rigid with respect to the compliant substrate, the strains are mainly concentrated in the substrate and less than 3% of the macroscopic stress is transmitted to the nanostructures.

Influence of mechanical and heat treatment on structure evolution and functional properties of Fe-Al-Tb alloys

The current research focuses on the microstructural analysis, damping, and magnetostrictive behavior of the Fe-12Al and Fe-21Al alloys doped with Tb after various mechanical and heat treatments. The thermomechanical treatment provides enhanced magnetostriction in both Fe-12Al and Fe-21Al with Tb addition. The maximal magnetostriction was observed in the alloys after hot rolling and subsequent 30 min annealing at 900 °C followed by air cooling. Tb increases the low temperature IF background and magnetostriction of Fe-21Al-Tb alloy.

Magnetostriction in -oriented composites with CoMnSi microspheres

CoMnSi exhibits weak mechanical performance and a low magnetostriction in polycrystals, which limits its potential magnetostrictive properties. Herein, we reported that a large reversible magnetostriction up to 1500 ppm in an oriented CoMnSi microspheres/epoxy resin composite. Textured CoMnSi microspheres (50–70 μm) were prepared in our designed nonwetting annealing method by dispersing the crushed particles into solid dispersions and melting them into spheres in a nonwetting environment. Facilitated by the spherical morphology, the <0kl> -oriented CoMnSi microspheres/epoxy resin composites with high volume fraction were produced in a 5 kOe uniform magnetic field. The uniform orientation and the high volume fraction of CoMnSi microspheres contribute to the large magnetostriction of CoMnSi composite. This work may provide a promising universal preparation method for spherical particles of intermetallic compounds and path a novel approach to optimizing property for magnetic material composites.

Exceptional combination of large magnetostriction, low hysteresis and wide working temperature range in (1-x)TbFe2-xDyCo2 alloys

Magnetostrictive materials with large magnetostriction, low hysteresis and wide working temperature range are desired for applications, but rarely obtained so far. In this work, we report a surprising finding in (1-x)TbFe2-xDyCo2 alloys: the composition of x = 0.5 exhibits a low hysteretic magnetostriction, λ||,max ∼2066 ppm, which is 1.59 times as large as that of the commercial giant magnetostrictive alloy of Terfenol-D, λ||,max ∼1298 ppm. Moreover, its temperature range for λ|| >1298 ppm is even larger than 240 K, and another working temperature window for λ|| >1000 ppm is from 40 K to 324 K, which can cover a large temperature fluctuation in space environments (e.g. 120-290 K in Mars). The established phase diagram of (1-x)TbFe2-xDyCo2 by systematic studies of magnetic susceptibility, X-ray diffraction and convergent-beam electron diffraction results, shows an emergence of morphotropic phase boundary (MPB) between rhombohedral (R) and orthorhombic (O) ferromagnetic phases, which is different from the MPB between R and T (tetragonal) phases in (1-y)TbFe2-yDyFe2. We reveal that the exceptional combination of giant magnetostriction, low hysteresis and wide working temperature range is caused by this R-O MPB. The comparison between R-O MPB and R-T MPB further shows the O phase plays a vital role in the property enhancement of R-O MPB composition. Our work indicates the construction of R-O MPB may provide a new way to find high-performance magnetostrictive materials.

Production of Fe-6.9 wt%Ti alloy sheets for application in electric machines: Physical properties characterization

Early structural damage and resulting failures can be caused by vibration in AC electrical machines. Since the stator is under a magnetic field that varies with time, the stator magnetic material contracts and expands due to the magnetostriction, producing noise and vibration. Therefore, a low magnetostriction value is desirable to minimize the effect of vibration and avoid earlier motor breakdowns. However, not only a low magnetostriction value is enough. Low values of magnetic losses avoid the material heating, consequently preventing magnetic properties degradation. To minimize these magnetic losses, a suitable material might have high resistivity and magnetic permeability, and also low coercive field. Fe-Ti alloys have low magnetostriction values and are soft magnetic material, making them good candidates for using in motors’ stators. In the present work, two Fe-Ti alloys with composition 6.9 wt% Ti (8 at.%) were studied. One of the alloys was studied after the as cast ingot annealing at 1200 °C. The other alloy was hot rolled from 7 mm down to 0.5 mm of thickness. The maximum magnetic induction of the rolled alloy was 1.74 T, about 12% higher than the not rolled one. In addition, the rolled Fe-Ti alloy magnetostriction is lower than 1 ppm up to 1.25 T, while in the not rolled condition is also 1 ppm, but only up to 0.75 T.

Experimental results of electromechanical structure properties of noise and vibration on power transformers after lightning impulse test

Transformer damage due to lightning impulse wave may result in serious loss of profits, thereby compromising the reliability of power systems. Currently, there is limited studies on the effect of lightning impulse on the noise and vibration of power transformers. In line with this, this study proposed a single-phase transformer with a voltage specification of 345 kV (high voltage)/115 kV (low voltage) and a capacity of 200 MVA. The soft magnetic 27PH100 material with a low magnetostriction variation was selected as the core material for the design of a transformer with a significantly low noise and vibration that could be maintained even after repeated lightning impulse applications. First, the parameters of the core and coil with k-factor design of the transformer, which can withstand high electrical signals, such as lightning impulses and insulation damage, was established and tested. The deformation and modal shape of the core and winding were simulated by finite element analysis. Furthermore, sweep frequency response analysis was used to observe the structure of the core and coil without any deformation. Diagnosis gas analysis was adopted to analyze the oil in the tank of the transformer to avoid dielectric loss due to insulation damage. Temperature rise test was also used to verify the stability of the transformer performance under no-load and full-load conditions. Finally, the results of the continuous lightning impulse tests revealed that the transformer operated under a stable performance, while generating significantly low noise (<65 dB) and vibration (<10 μm), which are remarkably lower than the IEEE standard of 85 dB.

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.