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Magnetic anisotropy, sress, and martensitic transformation in Ni-Mn-Ga thin films on Si(100) wafer

2007 MRS Spring Meeting.

Michael Haglera1, Volodymyr A. Chernenkoa2a3, Makoto Ohtsukaa4, Stefano Besseghinia3 and Peter M¨llnera1

a1 Materials Science and Engineering, Boise State University, 1910 University Dr., Boise, ID, 83725

a2 Institute of Magnetism, Kyiv, 03142, Ukraine

a3 CNR-IENI, Lecco, 23900, Italy

a4 IMRAM, Tohoku University, Sendai, 980-8577, Japan

ABSTRACT

Ni-Mn-Ga magnetic shape memory alloys (MSMAs) tend to undergo a large deformation upon the application of a magnetic field. This deformation is attributed to twin boundary motion in the martensitic phase. In an effort to harness the shape memory effect for use in sensors, actuators, and micro-devices, the behavior of Ni-Mn-Ga thin films is attracting attention. Substrate curvature measurements were done with Ni-Mn-Ga films with a thickness of 2.0 μm sputter-deposited on Si(100) wafer having amorphous 500 nm thick SiNx buffer layer. During the wafer bow curvature measurements, stress levels of 0.65 GPa were attained. The martensitic transformation is manifested by a stress-temperature hysteretic loop. Measurements of magnetization curves were carried out on Ni-Mn-Ga films with thickness between 0.5 and 3.0 μm. A change of the magnetization behavior from the easy-plane type for thin films to the out-of-plane easy-axis type for thick films is observed. This effect is caused by the interplay between different contributions to the overall anisotropy of film.

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