Electromagneto-thermo-mechanical functional ferromagnetic shape memory alloy

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We investigate a novel ferromagnetic shape memory alloy, Ni-Mn-Ga system, which has the shape memory effect induced by external magnetic field in addition to temperature and stress changes. We have obtained electromagneto-thermo-mechanical properties of this alloy that are important for the application of this alloy to actuators.For the bulk materials we have evaluated the material properties of this alloy changing the methods of heat treatment and fabrication procedures, and we have obtained the following results.1. Martensitic transformation temperatures and Curie points change for different Ni contents against the Mn. This change was verified by a differential scanning calorimeter (DSC) as well as magnetic properties and resistivity measurements.2. NiィイD22.18ィエD2MnィイD20.82ィエD2Ga shows a strange magnetic property that the structural transition and magnetic transition coincides at a certain temperature.3. The material made by an arc melting method was found brittle. We applied a spark plasma sputtering (SPS) method to this material and demonstrated that material properties were improved by this method.4. The alloy made by the SPS shows four times larger Young's modulus than that of the alloy made by an arc melting method.5. We measured the temperature dependency of the Young's modulus of this alloy fabricated by the SPS and found that the modulus changes with structural transitions of this alloy.For thin films we confirm the shape memory effect at certain film thickness and quench conditions made by a sputtering method. In this special heat treatment the crystal grain size becomes larger and the shape memory effect occurs when the temperature coincides with the transition temperatures measured by DSC. The shape memory effect of this film was demonstrated first in the world.