Shape memory and ferromagnetic shape memory effects in single-crystal Ni2MnGa thin films

Epitaxial Ni2MnGa and Ni2Mn1.2Ga0.8 thin films have been grown by molecular beam epitaxy on GaAs (001) substrates with Sc0.3Er0.7As interlayers. Structural characterization of as-grown films confirms the epitaxially stabilized single crystal structure of the films and indicates that the films grow pseudomorphically on GaAs (001) substrates in a tetragonal structure (a=b=5.65 A, c=6.18 A). The films are ferromagnetic at room temperature with coercivity of ∼50 Oe, saturation magnetization of ∼250 emu/cm3, and weak in-plane magnetic anisotropy. The Curie temperature of the films is found to be ∼340 K. However, while the films were attached to the substrate martensitic phase transformations were not observed. In order to observe martensitic phase transformations, free-standing Ni2MnGa bridges and cantilevers were fabricated using front and back side photolithography together with a combination of dry and wet etching. After removal of the substrate, the free-standing bridges and cantilevers showed a unique tem...

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