Abstract
Epitaxial Ni-Mn-Ga thin films with a room temperature martensite phase were fabricated on single crystal Al2O3(112¯0) substrate using direct current (DC) magnetron sputtering. The X-ray pole figure measurements confirm the epitaxial relationship of Ni-Mn-Ga (101)7M || Al2O3(112¯0) and Ni-Mn-Ga [101¯]7M || Al2O3[11¯01] between the film and substrate. Transmission electron microscopy reveals the presence of (220) micro-twins at an angle of 62.5° and 56.3° with respect to (202) growth plane. Coexistence of non-modulated martensite phase (aNM = 5.45 Å and cNM = 6.56 Å) and seven modulated martensite phases (a14M=6.26Å,b14M=5.89Åandc14M=5.56Å) has been observed in the film. The in-situ high-temperature X-ray diffraction indicates reversible thermal phase transformation in the film with a very low thermal hysteresis. The magnetic field induced reorientation (MIR) effect is displayed by the film.
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