Papers by Keyword: Magnetostriction

Abstract: Magnetron sputtering with a chromium-containing Fe-19at.%Cr alloy is used to improve the corrosion resistance of Fe-20at.%Ga alloy. The structure of the 2 μm coated layer and distribution of the elements (Fe, Cr, and Ga) are investigated. The bcc phase (A2 structure) is observed in the sputtered sample by XRD analysis. The corrosion resistance in 3.5%NaCl solution increases 14 times in the sample with 2 μm Fe-Cr coated layer. At the same time, the magnetron sputtering leads to a 10% decrease in magnetostriction and a 20% decrease in damping. This difference is explained by schemes of loading during magnetostriction and damping tests.

Abstract: The paper shows results of studying the effect of zero-to-tension cycling, with an amplitude approximately corresponding to the conventional yield strength, and subsequent static elastic tension along the same direction on the behavior of magnetostriction and differential magnetic permeability of low-alloy structural 08G2B steel. The behavior of the studied magnetic characteristics under static tension confirms the inference that the level of residual compressive stresses induced by cyclic preloading increases along the axis of cyclic tension.

Abstract: The performance of a vibration power generator using a single crystal core of Fe–Ga alloy was compared with that of a generator using a Fe–Ga alloy polycrystal core with a similar Ga concentration. When the generator using the polycrystal core was forcibly vibrated by 1-G acceleration, the vibration frequency dependence of the open-circuit voltage showed a peak with a maximum value of about 0.14 V at the first resonance frequency due to the inverse magnetostrictive effect. On the other hand, the generator using a single crystal core with a <100> direction parallel to the external stress direction exhibited a maximum value of about 0.26 V, about two-times larger than that of the device using the polycrystal core. Consequently, a vibration energy generator using a single crystal core of Fe–Ga alloy has advantages in performance over a generator using a polycrystal core.

Abstract: A comprehensive study of the structure and phase composition, magnetostrictive and magnetic properties of the (Sm_0.5R_0.5)Fe₂ (R = Gd, Tb) compounds was performed. The effect of partial replacement of samarium by gadolinium and terbium on the microstructure of the surface, the temperature of phase transitions, the magnitude of magnetostrictive deformations and magnetization was studied. Using atomic force and magnetic force microscopy, the surface topology at the micro and nanoscale was established, and information on the magnetic domain structure at room temperature was obtained.

Abstract: In magnetoelectric sensors for the detection of weak magnetic fields, the magnetostrictivecomponent is required to show a high strain at small magnetic field changes. Co-Fe alloys, amongrare earth free materials, have one of the largest saturation magnetostriction and are magnetically softat the same time. In this study, Co-Fe alloy films with 66 at.-% Co are prepared by magnetron sputterdeposition of Co/Fe-multilayers which differ in their individual layer structure and in a subsequentrapid thermal annealing process. The influence of the initial bilayer period and the annealing temperatureon the phase formation and film structure are investigated. X-ray diffraction revealed a higherfraction of the desired face-centered cubic solid solution for thicker individual layers after the 800 °Cannealing. The change of the electrical in-plane resistivity reaches a minimum around 500 °C and iscorrelating well with the observed grain growth and solid solution phase formation. The investigationof magnetic properties with vibrating sample magnetometry shows coercive fields of 3.2 kA/m and2.2 kA/m for fully alloyed films with initial bilayer periods of 25 nm and 250 nm, respectively.

Abstract: As-cast (Fe_0.83Ga_0.17)_100-xY_x (x=0, 3, 6 and 9) alloys were prepared by non-consumable vacuum arc melting furnace under a protective argon atmosphere. The crystal structures and surface morphologies of the alloys were studied by X-ray diffraction (XRD), optical microscope (OM) and scanning electron microscopy (SEM), combined with energy dispersive spectroscopy (EDS), respectively. The surface domain structures were observed by atomic force microscopy (AFM). The magnetostriction coefficients of the alloys were measured by strain gauging method. The results showed that the as-cast Fe₈₃Ga₁₇ alloy was composed only of a single phase of A2 with bcc structure, whereas the ternary Fe-Ga-Y alloys contain multiphase structure, besides the A2 phase, (FeGa)₁₇Y_1.76 new phases are observed as well, and an elemental yttrium phase appeared when the yttrium content increased to x=6 and x=9. Doping with yttrium have an effect on the change of magnetic domain structure of the binary alloy. With increasing x, the magnetostriction coefficient of the (Fe_0.83Ga_0.17)_100-xY_x alloys decreased sharply. The minimum magnetostriction coefficient is reduced to 12 ppm at the magnetic field of 426kA/m when x=9.

Abstract: For the first time hydroextrusion process was chosen for Fe-Ga ingots deformation with a gallium content of 19 and 20 at.%. The samples were annealed at 950oC, followed by air cooling. Structure of deformation and primary recrystallyzation were investigated by the method of electron back-scattered diffraction (EBSD). The degree of hydroextrusion deformation achieved was 28 – 42 %. There was not found any crystallographic texture at such degree of deformation. The value of magnetostriction in recrystallization sample was about 100 ppm. Available in literature methods and approaches to creation of the Fe-Ga samples from the point of view of receiving high magnetostriction and also a possibility of machining of the samples are discussed.

Abstract: The saturation value of the magnetostriction curve in the [100] direction of a Fe-Ga alloy single crystal was decreased from 226 to 55 ppm by applying the tensile strain of 533 ppm to the measured direction. By magnetic domain observation using a magneto-optic Kerr effect microscope, a complex structure composed of various magnetic domains was observed under zero applied strain. On the other hand, a stripe structure composed of magnetic domains with the magnetization direction in two kinds of <100> magnetic easy directions parallel to the tensile direction, which were separated by straight 180° domain walls, was observed under the tensile strain of 533 ppm. The characteristic magnetic domain structure due to the tensile strain was successfully observed as a cause of the significant decrease of the saturation value of the magnetostriction curve.

Abstract: Fe-Ga alloys are used for practical magnetostrictive materials. The understanding of mechanical properties under magnetic field is very important for their application to vibration power generation devices. Especially, Poisson’s ratio is one of key parameters because it is strongly related with the volume change of materials. In the study, we investigated actual behavior of Poisson’s ratio due to magnetostriction, instead of just the mechanical one. The sample was cube-oriented Fe-18mol%Ga single crystal disc. Static magnetic fields were applied in various directions parallel to (001). Strain values in various directions were measured by strain gauge and X-ray diffraction. And then, tri-axial strain analysis for single crystal was carried out. Theoretically, Poisson’s ratio due to magnetostriction is known to be 0.5, (volume conservative), value is close to the mechanical one, 0.45. On the other hand, we found that Poisson’s ratio exhibits anisotropic behavior despite the elastic constants are equivalent in [010] and [001]. This phenomenon is attributable to the magnetic domain structure under zero magnetic field. In this presentation, we will discuss this apparent Poisson’s ratio considering the volume strain and magnetostriction comprehensively.

Abstract: Fe-Ga alloy is expected as energy harvest material having superior magnetostrictive properties. In this study, we compared angle dependence of amount of magnetostriction with ideal magnetostrictive model using cube-oriented single crystal Fe-18mol%Ga alloy. Magnetostriction in [100] of specimen was measured with changing the direction of statical magnetic field H by strain gauge. As a result, the measured magnetostriction could not fully explaind by traditional energy-based model of magnetostriction. We compared measurement result using strain gauge with calculation result using energy-based model. As a result, there was a large difference in maximum compressive strain value. We established modified energy-based model considering the deviation of magnetic domains so as to match the actual magnetostriction behavior.