Evidence of adaptive modulation and magnetic field induced reorientation of variants in epitaxially grown Ni-Mn-Ga thin film on Al 2 O 3 (112¯0) substrate

Epitaxial Ni-Mn-Ga thin films with a room temperature martensite phase were fabricated on single crystal Al 2 O 3 (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 || Al 2 O 3 (112¯0) and Ni-Mn-Ga 101¯ 7M || Al 2 O 3 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 (a NM = 5.45 à and c NM = 6.56 à ) and seven modulated martensite phases (a 14M =6.26à ,b 14M =5.89à andc 14M =5.56à ) 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. © 201