In this study, the effects of surface treatments were investigated on the mechanical response of the LaNi5 thin film actuator deposited on polyimide substrates. Since controlling the hydrogen concentration in film by reversible pressure change drives this actuator, this film actuator can be expected as a sensor and/or a controller of hydrogen gas flux in various hydrogen-related devices. This significantly improved mechanical response was attributed to the switching of the reactions in the rate determining steps.
To develop an optical scanning device, the magnetostrictive alloy thin films were prepared on silicon wafer and polyimide substrate by d.c. magnetoron sputtering process. The TbFe1.8 film shows a giant positive magnetostriction of about 1200 ppm at 5 kOe, whereas the SmFe2.5 shows a giant negative magnetostriction of about 1200 ppm. The magnetostrictive alloy thin films device showed reproducibility below 5 kOe of magnetic field.
With increasing interest in micro machine and micro mechatronics, high interest is given to micro devices using magnetostrictive alloys with small sizes. The accurate measurement of magnetostritions ranging from several tens ppm to 1000 ppm of small alloy samples is not easy, and the establishment of measurement methods of magnetostriction of small samples is needed. In this study, four different methods were examined to measure magnetostrictions of small metal samples (cubic samples with sizes smaller than 5 mm x 5 mm x 5 mm ) : Optical interference (OI) method, cantilever (CL) method, strain gauge (SG) method and capacitance (CP) method. The OI method was found to have a high sensitivity, however, too sensitive to measure small deformations of a small sample because of mechanical disturbance induced by surrounding mechanical noises. The CL, SG, and CP methods exhibited similar values of magnetostriction with high stability and reproducibility. This paper reports and discusses results of these measurement methods.
In this study, the preparation of giant magnetostrictive Tb-Fe thin films by ion plating process was investigated to induce high magnetostrictive susceptibility and high magnetostriction, especially in respect to the effects of incidence of the vapor flux by geometrical arrangement of the tilted substrate. With increasing substrate angle of Tb-Fe films, the in-plane magnetization at 15 kOe was strongly increased. This indicates that the easy direction of magnetization of Tb-Fe film changed from perpendicular to in-plane by obliquely deposition. The magnetic and magnetostrictive characteristics of the obliquely deposited Tb-Fe films were affected by an oblique anisotropy. The oblique anisotropy of Tb-Fe film may be induced by the shape anisotropy connected with columnar grain.
Giant magnetostrictive (GM) composite materials with high corrosion resistance and high electrical resistivity were developed. Magnetostriction of the composite material prepared under magnetic field at 19 kOe was about 880 ppm, and the TbFe2 particle size in the sample was 100-150 μm. Shape anisotropy of the TbFe2 particles induced by compression and magnetic field caused to increase the magnetization and magnetostriction measured for y axis of the composite samples formed with magnetic field. The composite materials showed high resistivity in order to 10-2 Ωm and exhibited in order to 10-2 g hour-1 of corrosion rate. The corrosion rate of the composite samples increased with increasing TbFe2 particle size. The corrosion rate of the composite materials may be affected to volume fraction of the TbFe2 particles exposed area in surface of the composite materials.
Giant magnetostrictive (GM) Tb-Fe-Si films were prepared by magnetron sputtering system. X-ray diffraction pattern showed film samples were in amorphous state. The Tb-Fe-Si film (Tb : Fe : Si = 1 : 2.7 : 0.2) prepared at 373 K showed 30 MPa tensile stresses generated by magnetostriction along in-plane direction. The film sample showed about 4.3 μΩm of electrical resistivity that is about 100 times larger than that of TbFe2 film shown about 5.9 × 10-2 μΩm. The film sample coercivity was 360 Oe. Magnetization of the film sample at 15 kOe of applied magnetic field in parallel direction to the film surface exhibited 81.0 emu/cc. We prepared giant magnetostrictive thin film with higher electrical resistivity than that of TbFe2 thin film.
New high responsive Fe-Pd magnetostrictive films with high power were developed and prepared by magnetron sputtering. The in-plane magnetization of Fe-Pd thin film was larger than that of the Tb0.3Dy0.7Fe2 alloy film. The Fe-Pd magnetostrictive films show large magnetostriction and high magnetostrictive susceptibility at low magnetic field from earth magnetic field to 1 kOe. The high magnetostrictive susceptibility of the Fe-Pd alloy films obtained was appropriate as a remote actuator in low magnetic field. If an ideal Fe-Pd magnetostrictive films are developed to apply the micro-machine, offering the advantages of low cost, lightweight and relatively simple design. In order to
apply these properties to a practical actuator, load dependence of magnetostrictive susceptibility was serious potential problems. In this study, the magnetostrictive susceptibility changes were measured under different loading stresses. As a result, Fe-Pd alloy film showed high magnetostrictive susceptibility under high film loading stress above 50 MPa.
The crystal growth of Tb-Fe giant magnetostrictive materials under microgravity (μG) and terrestrial gravity (1G) was investigated. The microgravity conditions were obtained by free fall in drop tower facility at the Japan Microgravity Center (JAMIC). TbFe1.83 alloy with 1 gram and cubic form was prepared for unidirectional solidification under microgravity environment. The samples were melted just before drop and solidified by contact chill against a sample at the period of microgravity after dropping. The microstructure of μG sample was columnar structure and growth direction was aligned in thermal gradient. In 1G sample, the microstructure was weak aligned in thermal gradient. The composition was measured by EDX. The TbFe3 phase was observed in 1G sample, and no TbFe3 phase was observed in μG sample, caused by reduction of thermal convection in microgravity environment. In μG sample, the columnar structure that aligned thermal gradient was oriented orientation. The magnetostriction of parallel direction to the thermal gradient was larger than perpendicular direction in μG and 1G. The magnetostriction of μG sample, the measurement direction was parallel to the thermal gradient, was larger than 1G sample caused by microstructure.
Three types of magnetic field operated shape memory ceramics have been developed. Namely, the shape memory movements can be operated by changes in magnetic flux density. The reversible shape memory effects are often induced by magnetostriction and magnetic field induced twin formation for Fe-Pd alloys. The former shows the precise shape change, whereas the later shows the large shape change expected. The strain value was about 182 ppm at 0.3 kOe at room temperature. The high magnetostrictive susceptibility was detected at low magnetic field. It was higher than that of Tb0.3Dy0.7Fe2 thin film developed. The other magnetic field operated shape change is recently found on softening near critical temperature of superconductors. The softening induced shape memory effect (SSME) has been found from 9.5 K to 20 K in pure metallic niobium.
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