Abstract
Epitaxial Ni-Mn-Ga thin films have been extensively investigated, due to their potential applications in magnetic micro-electro-mechanical systems. It has been proposed that the martensitic phase in the <1 1 0>A-oriented film is much more stable than that in the <1 0 0>A-oriented film. Nevertheless, the magnetic properties, microstructural features, and crystal structures of martensite in such films have not been fully revealed. In this work, the <1 1 0>A-oriented Ni51.0Mn27.5Ga21.5 films with different thicknesses were prepared by epitaxially growing on Al2O3(1 1 0) substrate by magnetron sputtering. The characterization by X-ray diffraction technique and transmission electron microscopy revealed that all the Ni51.0Mn27.5Ga21.5 films are of 7M martensite at the ambient temperature, with their Type-I and Type-II twinning interfaces nearly parallel to the substrate surface.
Highlights
IntroductionAcademic Editor: Rositsa YakimovaNi-Mn-based ferromagnetic shape memory alloys have been considered as the promising materials for magnetic field-driven sensors and actuators, new type solid state refrigeration, and thermomagnetic generators [1–12]
Ni-Mn-based ferromagnetic shape memory alloys have been considered as the promising materials for magnetic field-driven sensors and actuators, new type solid state refrigeration, and thermomagnetic generators [1–12]
The magnetically induced reorientation of martensite variant has been reported in the A -oriented Ni-Mn-Ga thin films epitaxially grown on the MgO(1 0 0) substrate and NaCl (1 0 0) substrate
Summary
Academic Editor: Rositsa YakimovaNi-Mn-based ferromagnetic shape memory alloys have been considered as the promising materials for magnetic field-driven sensors and actuators, new type solid state refrigeration, and thermomagnetic generators [1–12]. Under the external magnetic-, thermal-, and force-field stimulus, they usually occur martensite variant reorientation and/or martensitic transformation [9–12], exhibiting multi-functionalities such as giant magnetic fieldinduced strain [1–5], excellent magnetocaloric effects [6–8], and colossal elastocaloric effects, etc. Among these functionalities, the giant magnetic field-induced strain has gained much attention, since both the single crystalline and polycrystalline bulk materials have demonstrated giant magnetic field-induced strain as much as 6–12% and 1% [1–5], respectively. Magnetic field-induced strains have not been achieved yet, since these kinds of thin films are of single crystalline state in the Austenite at evaluated temperatures and transform to self-accommodated martensite at ambient temperature. The self-accommodated martensite microstructure always contains two kinds of distinct microstructures: Type-X and Type-Y, which is composed of several different oriented martensite variants [17,24,25]
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