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Several ways to adjust structural and physical properties of Ni-Mn-Ga thin films obtained by r.f. sputtering
|Florent Bernard 1, Christophe Rousselot 1, Laurent Hirsinger 2, Patrick Delobelle 2|
1. Institut FEMTO-ST, Dpt LPMO, BP 71427, Montbéliard Cédex 25211, France
The aim of this communication is to present Ni-Mn-Ga thin films elaborate by r.f. sputtering with low power (less than 120W) and from Ni2MnGa alloy target. Chemical composition, crystallographic structure identified from DRX, surface morphology from AFM, internal stress, nanoindentation modulus and strain induced by magnetic field of these films are systematically investigated as a function of the sputtering parameters (Argon pressure and power), the sputtering temperature (from 298 to 1073K) and the annealing treatment (from 473 to 873K). The films deposited at room temperature have nearly Ni55Mn23Ga22 constant chemical composition, and, DRX analyses show 2 phases (one of them has a martensitic structure) that turn into only one phase when annealing temperature is increased. These results are confirmed by nanoindentation tests performed with few nm penetration depths. The set of these measurements give histograms with 2 indentation moduli M (respectively 135 and 210GPa) for films deposit at room temperature. These moduli decrease progressively with the annealing temperatures to reach at 873K a unique value of 97GPa also obtained in bulk ferromagnetic shape memory alloy (FSMA). Moreover, the internal stress in films deposited on Si beam cantilever is identified as a function of various sputtering conditions. It reveals three different areas delimited by 473K and 673K sputtering temperatures with a maximum stress value of 1,7GPa reached at 673K. Finally, the strain induced by magnetic field is measured via the deflection of the coated Si cantilever beam and a maximum strain value of -340ppm is reached for 1e6A/m magnetic field applied on films annealed 6h at 873 K. In conclusion, these results obtained from different techniques are coherent and consistent with the ones available in the literature. They show that the annealing treatments bring on an important transformation beginning at about 673K to finally give the FSMA properties to films from about 873K.
Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Laurent Hirsinger
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-18 17:39 Revised: 2009-06-07 00:44