Fabrication and Characterization of Ni-Mn-Ga Microdots
Modulated martensite of off-stoichiometric Ni-Mn-Ga magnetic shape-memory alloy has been of particular interest due to low stresses required for magnetic-field-induced strain (MFIS) which is tied to the large magnetic anisotropy of the martensite structure and the high mobility of twin boundaries. Grain boundaries of polycrystalline structures hinder twin boundary motion and thus MFIS. Controlling the grain size and reducing the scale of samples can reduce the hindrance of twin boundary motion. To explore controlling these constraints, Ni-Mn-Ga thin films and microdots were fabricated and characterized for composition, microstructure, and magnetic properties. The magnetic force microscopy contrast of the microdot indicated out-of-plane magnetization of the predominant crystallographic c-direction. X-ray diffraction indicated a <211> fiber texture. The microdot magnetic domain size is on the same order of the grain size found in the TEM micrographs which suggests that the magnetic contrast of MFM is indicative of individual grains. If microdot size can be reduced, this process could create thin film single crystals that are easier to produce and manipulate for various applications.
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