Giant Magnetostriction On Melt-Spun Ribbons And Exploring New High Chemical Ordering Alloy

Large magnetostrictions of -1300 and +1100 ppm have been obtained in our Fe85Ga15 ribbon samples. In the case of non-180° domain magnetization in the high anisotropic samples, the magnetostrictions are mainly attributed to the existence of Ga clusters which preferentially orient with the ribbon normal due to the ribbon grain texturing. Forming the modified DO3 structure, the Ga-Ga atom pairs distribute in the matrix and cause the x-ray diffraction peak split in melt-spun ribbons. As a special micromorphology, Ga clusters highly condensed in some nanoscale dots have also been experimentally observed by TEM examinations.In addition, a series of 6 samples with compositions Fe100-xGax (x=85,83,80,75,73,72) were prepared by melt-spinning technique to systemically investigate the magnetic properties, such as, magnetostriction, magnetization and Curie temperature. XRD examination was performed for these alloys to reveal the relation between ribbon structure and the composition. The samples exhibit large saturation magnetization in the composition range, which achieve the magnetostriction at easily attainable fields. The temperature dependence of magnetostriction and the effect of angle are also discussed. A small increase of magnetostriction with increasing temperature was observed between 163 and 321K. However, in higher temperature, the magnetostriction increases sharply with increasing temperature.We report on the detailed observation of martensitic variants in NiMnGa single crystals. The variants that are twinned with each other in different ways can be clearly identified in our single crystals by optical observation. We also investigated the preferential orientation of the martensitic variants in NiMnGa single crystals. We observed the motion of the variant boundary in response to application of a magnetic field. This observation can be used to explain phenomenologically the magnetic-field-induced strain. In the single crystal with composition Ni52Mn24Ga24, martensite with seven modulated layers (7M) shows preferentially orientedvariants. A completely recoverable two-way shape-memory behavior was also observed by measuring the free sample in three different directions during a complete temperature cycle. It was found that the largest strains in the [001] and [010] directions occur in different temperature ranges.A lot of alloys with the formula of X2YZ have been prepared by melt-spinning technique because of the possibility to be imposed high chemical ordering on them. Structures of the alloys have been investigated by means of X-ray diffraction and TEM observations. It was found that the structure of high chemical ordering was imposed on Mn2FeSn, Mn2FeGa, Co2NiGa, Fe2MnAl and Ni2FeGa by cooling rapidly, and the alloys with high chemical ordering are impossible to be produced by conventional method. We investigated the magnetic properties and transport properties, such as, ac susceptibility, magnetization, Curie temperature and magneto resistance. The investigated results revealed some remarkable phenomena and lay a foundation for future investigation on the alloys of high chemical ordering.