Fig. 1. Room temperature XRD patterns of Ni50.3Mn28.2Ga21.5 thin films on MgO(0 0 1) substrate, with the azimuth angle positions with PHI equal to 0°(a) and 45°(b).

Fig. 2. (a) BSE images of Ni50.3Mn28.2Ga21.5 thin films grown on MgO(0 0 1) substrate. (b) Magnified view of the yellow rectangular region in (a). (c, d) Illustrations of martensite variants, twin interfaces, and easy magnetization axes (black arrows) in the Type-Y and Type-X regions.

Fig. 3. (a) M-H loops of Ni50.3Mn28.2Ga21.5 thin films grown on MgO(0 0 1) substrate, measured along the out-of-plane direction (H//[001]MgO) as well as the in-plane directions (H//[100]MgO, H//[010]MgO and H//[110]MgO). (b) Zoomed view of the graphs at low magnetic fields in (a). The abrupt magnetization change can be observed in the M-H loops with the applied magnetic fields along [100]MgO and [010]MgO directions, where the magnetic fields for abrupt changes in magnetization are marked by blue and green arrows, respectively.

Fig. 4. (a) Low magnification optical image of Ni50.3Mn28.2Ga21.5 thin films grown on MgO(0 0 1) substrate, showing two differently oriented Type-Y regions and two differently oriented Type-X regions. The traces of twin interfaces within the Type-Y1 and Type-Y2 regions are parallel to the [100]MgO and [010]MgO directions, respectively. The traces of twin interface within the Type-X1 and Type-X2 regions are parallel to the $[1\bar{1}0]$MgO direction and [110]MgO direction, respectively. The traces are indicated with the dotted lines. The dashed rectangular regions are the selected region to extract M-H loops. (b) M-H loops of the whole region, (c) Type-Y1 region and Type-Y2 region, and (d) Type-X1 region and Type-X2 region, extracted from Kerr magnetometric measurements with the applied magnetic field along the [010]MgO direction.

Fig. 5. (a) M-H loops of the Type-Y2 region measured by Kerr magnetometry (green curve) and variation rate of region fraction of the darker contrast domains in (b) with the variation of the applied magnetic field. The magnetic field is applied along the [010]MgO direction, which is parallel to the twin interfaces. (b) Point-wise domain images recorded at selected magnetic fields as indicated in (a). The red and blue arrows represent the magnetization direction of the magnetic domains. (c) Schematic illustration of the magnetic domain evolution during the magnetization process on a local scale.

Fig. 6. (a) M-H loop of the Type-Y2 region measured by Kerr magnetometry. The magnetic field is applied along the [100]MgO direction, which is perpendicular to the twin interfaces. (b) Point-wise domain images recorded at selected magnetic fields as indicated in (a). The red and blue arrows represent the magnetization direction of the magnetic domains. (c) Schematic illustration of the magnetic domain evolution during the magnetization process on a local scale.

Fig. 7. Magnetic domains of the Type-Y zone in the Ni50.3Mn28.2Ga21.5 thin film after AC demagnetization with field along the [010]MgO (a) and [100]MgO (b) directions. The correspondent domain schematics are presented on the right side. The magnetization sensitivity of the Kerr-microscope is along the horizontal direction ([100]MgO direction) with respect to the image plane.

Fig. 8. Illustration of magnetically induced reorientation of martensite variants in the Type-Y2 region. (a) Ground state with two twin-related martensite variants. (b) MIR occurred partially in Variant 2. (c) MIR occurred fully in Variant 2. Wy and Ly are the width and length of the illustrated region, respectively.

Fig. 9. (a-d) Optical microstructures of Type-Y2 region under different magnetic fields. (e-f) Brightness spectra extracted from the corresponding lines and columns indicated in (a) at different magnetic field intensities. The distances between the selected peaks are indicated.