IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Microelectromechanical Systems (MEMS) Thursday Sessions
       Session MM-ThM

Paper MM-ThM8
MBE-grown Single-crystal Ferromagnetic Shape Memory Ni@sub 2@MnGa Thin Films

Thursday, November 1, 2001, 10:40 am, Room 130

Session: Characterization of MEMS Materials
Presenter: J.W. Dong, University of Minnesota
Authors: J.W. Dong, University of Minnesota
J. Lu, University of Minnesota
J.Q. Xie, 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
Ni@sub 2@MnGa is a ferromagnetic shape memory alloy which goes through a thermodynamically reversible martensitic phase transformation and demonstrates ferromagnetic properties. In bulk, Ni@sub 2@MnGa with the stoichiometric composition has a Curie temperature ~376 K and the martensitic phase transformation occurs ~202 K. Above 202 K, Ni@sub 2@MnGa adopts a cubic L2@sub 1@ crystal structure with weak magnetic anisotropy. Below 202 K, it will transform to a tetragonal structure with greatly enhanced magnetic anisotropy. In this low-symmetry tetragonal phase, a twinning structure will be formed by three types of martensitic variants with different magnetic easy axes. External magnetic and/or stress fields can be employed to adjust the volume fraction of the twinned martensitic variants by the motion of twin boundaries. This will result in large reversible strain and this novel mechanism is thus called ferromagnetic shape memory effect. In bulk single crystals of Ni@sub 2@MnGa, strain as large as 6.1% has been demonstrated. This makes it a promising candidate for magnetic field driven actuator material. For micro-electro-mechanical-system (MEMS) actuators, conceptual designs based on single-crystal Ni@sub 2@MnGa films have been proposed. The first single-crystal growth of Ni@sub 2@MnGa thin film has been reported by the authors.@footnote 1@ The 300 Å-thick film grows pseudomorphically on a (001) GaAs substrate with a unique tetragonal structure (a = b = 5.65 Å, c = 6.12 Å). The Curie temperature was measured to be ~320 K. Moreover, martensitic phase transformation is observed in a partially released 450 Å-thick epitaxial film. In this presentation, we will report the growth, characterization, and patterning of 900 Å-thick single-crystal Ni@sub 2@MnGa films to elucidate the concept of using it in MEMS actuators. @FootnoteText@ @footnote 1@ J.W. Dong, L.C. Chen, C.J. Palmstrom, R.D. James, and S. McKernan, Appl. Phys. Lett., 75, pp. 1443-1445 (1999).