AVS 49th International Symposium
    Microelectromechanical Systems (MEMS) Thursday Sessions
       Session MM+TF-ThM

Paper MM+TF-ThM7
Free-standing Single-crystal Ni@sub2@MnGa Thin Films: A New Functional Material for MEMS

Thursday, November 7, 2002, 10:20 am, Room C-210

Session: Development and Characterization of MEMS Materials
Presenter: C.J. Palmstrom, University of Minnesota
Authors: J.W. Dong, University of Minnesota
J.Q. Xie, University of Minnesota
J. Lu, University of Minnesota
Q. Pan, University of Minnesota
J. Cui, University of Minnesota
S. McKernan, University of Minnesota
R.D. James, University of Minnesota
C.J. Palmstrom, University of Minnesota
Correspondent: Click to Email
Ferromagnetic shape memory (FSM) alloys are a new type of materials that experience thermodynamically reversible martensitic phase transformations and demonstrate ferromagnetic property. This ferromagnetic property provides unique handle on the configuration of the martensitic phases. Practically, moderate external magnetic/stress field can be applied to the FSM alloys in the twinned martensitic phase to adjust the volume fraction of the variants by the motion of twin boundaries, which will yield macroscopic shape change. In bulk single crystals of Ni@sub2@MnGa, a typical FSM alloy, strain as large as 9.5% has been demonstrated.@footnote 1@ This makes Ni@sub2@MnGa a promising candidate for magnetic field driven actuator material. For micro-electro-mechanical-system (MEMS) actuators, several conceptual designs based on single crystal Ni@sub2@MnGa films have been proposed.@footnote 2@ The first single crystal growth of Ni@sub2@MnGa thin film has been reported in ref. 3. The 300 Å-thick film grows pseudomorphically on a GaAs (001) substrate (a = b = 5.65 Å, c = 6.12 Å) and has a Curie temperature ~320 K. Furthermore, 900 Å-thick single-crystal Ni@sub2@MnGa films have been processed into free-standing bridges and cantilevers.@footnote 4@ The free-standing cantilevers show two-way shape memory effect under repeated thermo-cyclings. In this presentation, focus will be put on the shape memory effect and the magnetic field induced strain in the free-standing Ni@sub2@MnGa films to elucidate the concept of using it as a new functional material in MEMS design. @FootnoteText@ @footnote 1@ A. Sozinov, et al., Appl. Phys. Lett., 80, 1746 (2002). @footnote 2@ K. Bhattacharya, et al., Mat. Sci. Eng. A, 275, 685 (1999).@footnote 3@ J. W. Dong, et al., Appl. Phys. Lett., 75, 1443 (1999).@footnote 4@ Q. Pan, et al., to be published in J. Appl. Phys.