Papers by Keyword: Magnetostriction

Abstract: Grain growth and grain boundary character distribution relationships in Fe-Ga rolled sheet is investigated to study the influence of H₂S gas content in argon on the development of selective grain growth through secondary recrystallization. Abnormal growth of (011) grains was predominant at the low content of H₂S gas, while (113) grain growth was well developed at contents higher than 1.33% H₂S. On the other hand, the development of (001) grains was challenging to produce because it is very sensitive to the anneal environment and has a relatively low fraction of high energy grain boundaries associated with misorientation angles that determine the mobility of boundaries.

Abstract: We carried out in situ tri-axial magnetostriction analysis for cube-oriented Fe-18%Ga single crystal by X-ray diffraction measurement under magnetic field. Periodic change in tri-axial magnetostriction with applied magnetic field direction was clearly observed. However, those values in [100] and [010] directions were not equivalent. Theoretical calculation of magnetostriction considering domain structure revealed this is caused by the non-equivalent volume fraction of initial magnetic domains.

Abstract: Fe-Ga alloys show large magnetostriction, which strongly depends on crystal orientation. This phenomenon is associated to some degree with large elastic anisotropy. In this study, white X-ray diffraction with micro-beam synchrotron radiation was used to evaluate the microscopic stresses evolved in a polycrystalline Fe-Ga alloy under tensile loading. In the analysis, the large elastic anisotropy of the Fe-Ga alloy was focused. The stress distribution in the alloy microstructure under tensile loading was estimated using a finite element method (FEM) simulation that considered the dependence of the elasticity on the crystal orientation. The crystal orientation of grains in the polycrystalline Fe-Ga alloy was measured using electron backscatter diffraction. The FEM simulation showed that the stress distribution in the microstructure depended on the crystal orientation. The X-ray diffraction stress analysis indicated that under tensile loading, the stresses in the alloy depended on the crystal orientation. This finding is similar to the results obtained from the FEM simulation, although the absolute values of the stresses may have reflected the effects of heterogeneous deformation on the stress distribution.

Abstract: We carried out in situ x-ray diffraction measurements of magnetostriction in an Fe-18at%Ga alloy single crystal under magnetic fields. The sample studied here was a Goss-oriented square plate (dimensions: 10 mm × 10 mm × 1 mm height) cutting from as-grown single crystal ingot produced by the Czochralski method. In-plain magnetic fields were applied with various directions in this study. The influence of magnetic field direction on the stress/strain states was precisely analyzed by using our original x-ray single crystal stress/strain measurement method. As a result, applied field angle dependence of tri-axial magnetostriction states was successfully obtained. Thereby, we found that the singular anisotropic mechanical properties of this material play an important role for its magnetostriction properties.

Abstract: A combination study of magnetic and magnetostrictive properties in directionally cast and differently heat-treated Fe-20Ga(at.%) samples has been carried out at room temperature. Slow cooling leads to an increase in the occupation of [200] easy magnetic axes; however, a structural ordering of Ga atoms into a metastable D03 phase decreasesthe saturation magnetostriction (λs) and the saturation magnetization (Ms), and increases coercivity (Hc).Our results confirm the contribution of D03 ordering to magnetic and magnetostrictive properties due to their pinning effects against magnetic domain wall motions. As compared to slow cooling, water quenching suppresses the formation of metastable (D03) or stable (L12) ordered phases and preserves the A2 single phase structure down to room temperature, leading to enhanced magnetostriction and magnetization.

Abstract: Recently, one can observe increasing number of small devices or sensors in many applicationsthat have to be powered by an energy which can be extracted from surroundings. Simple energyharvesting concept from mechanical vibrations of magnetostrictive materials is based on linear beamwith external excitation. In this case, the beam under load vibrates, and experiences stress or strain.This changes the beam shape which causes direction of sample magnetization (Villari effect) thatcan be captured by external coil and transferred to electrical power. In general, the higher amplitudeof beam vibrations, the higher energy can be extracted from the system. This can be achieve in thevicinity of a resonant frequency. In this paper, we propose energy harvesting model based on linearmagnetostrictive (MsM) beam with external coil. We analyse different shapes of the beam withrespect to different resonant frequencies.

Abstract: Mn_100-xFe_x (x=50, 58) alloys were prepared by spark plasma sintering (SPS), and the structure, magnetostriction and magnetic properties of the polycrystalline Mn_100-xFe_x alloys were investigated. The results of XRD and SEM showed that the as-cast and annealed samples presented a single face center cubic γ-phase, which is austenite structure. The magnetic measurement showed that Mn_100-xFe_x (x=50, 58) alloys annealed at 700^oC were a typical ferromagnet at low temperature and there was a gradual transition from the ferromagnetic phase to the paramagnetic phase in a wide temperature region (about 150-250K). The magnetostriction for the annealed samples, measured by strain-gauge bridge up to 3T, was ~100 ppm at 300K, but the results was chaotic. The results are not in agreement with the results reported. The further research on the mechanism of the magnetostriction is needed.

Abstract: The purpose of this work was the complex investigation of magnetic, magnetocaloric and magnetoelastic properties of compounds based on Gd₅Si₂Ge₂ with small In substitutions in p-sublattice. The conducted measurements revealed that both the magnetocaloric effect and the volume magnetostriction upon cooling reach the higher values than upon heating. Indium substitution leads to the appearance of the second maximum on the temperature dependence of the magnetocaloric effect resulting in the increase of the refrigerant capacity.

Abstract: The magnetic anisotropy (MA) of trihydrides of single-crystalline rare-earth (R) intermetallics R₂Fe₁₇H_3±x (R = Tb and Dy) with small deviations in the hydrogen concentration (x = 0 – 0.4) was investigated via the magnetic and magnetoelastic measurements in a wide temperature region. The easy-axis MA of Tb₂Fe₁₇H_3±x is preserved in the entire range of magnetically ordered state while an “easy-cone – easy-plane” transition takes place in Dy₂Fe₁₇H_3±x above ambient temperatures. The trihydrides demonstrate a significant decrease of magnetic anisotropy as the temperature increases. The temperature variation of thermal expansion of Dy₂Fe₁₇H₃ displays anomalies in the vicinity of a spin-reorientation transition. The longitudinal magnetostriction λ_||(T) of the same compound changes its sign at 340 K. The compounds studied can find specific applications in practice.

Abstract: We have designed a magneto-optical sensor based on fiber Bragg grating (FBG) and Metglas 2605CO (Fe₆₇Co₁₈B₁₄Si₁) material with magnetostriction coefficient of 35ppm. The FBG sensor is glued between two sheets of Metglas. FBG-based detectors are sensitive to both temperature changes (approximately 10pm/°C) and mechanical stress (approx. 1.15pm). Also due to the thermal expansion of Metglas, it becomes imperative to isolate the joint effects of thermal expansion of Metglas and the FBG temperature drifts. This is achieved by introducing an additional FBG used as a temperature sensor. We have characterized the responses of the sensor in two directions simultaneously: parallel and perpendicular to the direction of the applied magnetic field.