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Residual stress in Ni-Mn-Ga thin films deposited on different substrates
|Stephen Doyle 1, Volodymyr A. Chernenko 2, Stefano Besseghini 3, Andrea Gambardella 3, Manfred Kohl 4, Peter Mullner 5, Makoto Ohtsuka 6|
1. Forschungszentrum Karlsruhe GmbH, Institut für Synchrotronstrahlung, ANKA (ANKA), Hermann-von-Helmholtz-Platz 1, Karlsruhe 76344, Germany
Great attention has been recently paid to the development and study of MSM Ni-Mn-Ga/substrate thin film composites. The workability and reliability of small-scale devices utilizing such materials is highly dependent on the residual stress which such thin films exhibit due to the thermal expansion and lattice mismatches.
In the present work we report on residual stress measurements by X-ray diffraction in the standard θ/2θ Bragg-Brentano geometry carried out at the ANKA synchrotron facility (FZK, Karlsruhe). In the method commonly known as “sin2ψ", the lattice spacing is assumed to be a linear function of sin2ψ, where ψ is the angle between the diffracting plane normal and specimen surface normal. A biaxial plane-stress model is then used to convert the measured strain into stress.Four series of Ni51.4Mn28.3Ga20.3/substrate thin film composites, where the substrates are either Si(100), MgO(100), alumina or molybdenum foil, and three series of Ni53.5Mn23.8Ga22.7/substrate composites where the substrate is either Si(100), alumina or Mo foil, with different film thicknesses varying from 0.1 to 5μm have been studied in the cubic phase by XRD stress measurements. An analysis of the results was made assuming the value of Young modulus and Poisson ratio to be equal to 50 GPa and 0.3, respectively, for all the films. The zero-stress lattice spacing was determined from the condition of sin2ψ = 0. The estimated level of residual stress is found to vary from 0.12 GPa for the 1 μm-thick film on MgO(100) to 0.53 GPa for the 0.1 μm-thick film on Si(100). In addition, a weak thickness dependence of stress is observed for films on MgO or Mo while it is much stronger and has the opposite sign for films on alumina or Si(100). The results are relevant to the evaluation of stress-induced magnetic anisotropy of films.
Presentation: Poster at E-MRS Fall Meeting 2007, Symposium E, by Stephen Doyle
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-14 17:09 Revised: 2009-06-07 00:44