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Phase Transformation and Optical Reflective Properties of Ni-Mn-Ga-Gd Alloy Thin Films

Author: LuQingCui
Tutor: CaiWei
School: Harbin Institute of Technology
Course: Materials Physics and Chemistry
Keywords: Ni-Mn-Ga-Gd alloys crystallization martensitic transformation optical reflectance
CLC: O484.4
Type: Master's thesis
Year: 2008
Downloads: 18
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Abstract


Ni-Mn-Ga-Gd alloy thin films have been successfully deposited on (100)-Si substrates by magnetron sputtering technique. The effects of sputtering parameters and crystallization process on phase structure, chemical compositions and surface morphology have been systematically investigated by means of XRD, EDAX, SEM and AFM. Martensitic transformation characterization and dynamic mechanism of Ni-Mn-Ga-Gd thin films under different rapid heating and cooling enviorment have been obtained. At the same time, the effect and mechanism of surface state and phase structure on optical reflectance have been revealled.The results show that the sputtering technical parameters have obvious influence on chemical composition. The content of rare earth Gd in the Ni-Mn-Ga-Gd alloy thin films decreases with the pressure inceasing and sputtering power fixed. With the sputtering power increasing, the contents of Ni and Mn decrease, however, the content of Ga dramatically increases in Ni-Mn-Ga alloy thin films.The experimental results indicate that Ni-Mn-Ga-Gd alloy thin films are partially crystallized before heat treatment by the result of XRD. After annealing at 550℃for 1 hour, crystallization activation energy of Ni-Mn-Ga-Gd alloy thin film is 183.7KJ/mol. After annealing, the samples of Ni46.0 Mn27.1Ga25.6Gd1.3, is parent phase state with body-central cubic L21 structure; the film of Ni47.4Mn26.3Ga24.8Gd1.5 and Ni52.6Mn24.6Ga22.8 are 5M martensitic phase,at room-temperature; Ni55.37Mn25.70Ga18.93 is T martensite and Ni54.6Mn24.6Ga20.8 is 7M martensite.The results show that the martensitic transformations activation energy decreases with increasing annealing rate. The second martensitic transformations generation is higher than that of the first with the same annealing rate.The optical characteristics results of Ni-Mn-Ga-Gd alloy thin film indicate that, in the wavelength range of 200nm～850nm, the reflectances increase with incident wavelength increasing. The lower root-mean-square roughnee of Ni-Mn-Ga-Gd alloy thin films, the higher the optical reflectance. The optical reflectance of the film which is martensitic phase is higher than that of the film which is parent phase. The different films which are different martensitic phase and same parent phase have the different optical reflectance. At the blue light wavelength 400nm, the two-phase optical reflectance difference is 7% on the film of 5M martensitic phase; the two-phase optical reflectance difference is 10% on the film of 7M martensite and 17% on that of T martensite.

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CLC: > Mathematical sciences and chemical > Physics > Solid State Physics > Thin Film Physics > The nature of the films
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