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Materialien/Werkstoffe Poster: Do., 13:00–15:30 D-P379
Texture of submicron Ni-Mn-Ga films studied by X-ray beam line of synchrotron
source
Volodymyr Chernenko 1 , Stephen Doyle 2 , Manfred Kohl 3 , Peter Müllner 4 ,
Stefano Besseghini 5 , Makoto Ohtsuka 6
1 Institute of Magnetism, Vernadsky str. 36-b, Kiev 03142, Ukraine – 2 ANKA,
Forschungszentrum Karlsruhe, D-76021, Karlsruhe, Germany – 3 IMT, Forschungszentrum
Karlsruhe, D-76021, Karlsruhe, Germany – 4 Department of Materials Science
and Engineering, Boise State University, Boise, ID, USA – 5 CNR-IENI, Lecco 23900,
Italy – 6 IMRAM, Tohoku University, Sendai 980-8577, Japan
The ferromagnetic thermoelastic martensites exhibited by the single and polycrystalline
Ni-Mn-Ga alloys have attracted much attention as potential multifunctional
materials.It is a challenge to develop thin film technology for the production of microand
nanocrystalline Ni-Mn-Ga martensites and to keep their functionality as in the
bulk. In general, because the properties of polycrystalline thin films depend strongly
on their microstructure, an important research area is concerned with the control of
this microstructure, in particular the texture and internal stresses which develop during
deposition and post-deposition annealing processes. As much as the feasibility of
magnetomechanical activation in polycrystalline films is concerned, the crucial point is
to get them in a crystallographic oriented (textured) form.The preferable orientation
of one crystal axis in grains would give rise to the overall magnetic anisotropy of film
as a prerequisite of its macroscopic magnetomechanical response. In metallic films,
texture and martensitic transformation depend on the film thickness.
In this work, we used an X-ray diffraction facility attached to the beam line generated
by ANKA synchrotron source, FZK, Karlsruhe to study a texture and internal stress
problem in Ni-Mn-Ga thin films magnetron-sputtered on alumina ceramic and molybdenum
foil. Series of film/substrate composites with film thicknesses ranging from 0.1
to 5.0 micrometer were fabricated using two targets of different compositions. Films
on substrates were vacuum annealed at 1073 K for 36 ks. The target compositions were
designed to get in annealed films a 5-layered tetragonal and 7-layered orthorhombic
martensitic phases, respectively.
X-ray diffraction mapping was made at 300 and 423 K. An in-house made temperature
controlled heating unit was designed to this aim. The selected values of temperatures
assured our films to be either in martensitic or austenite cubic state. The texture
measurements were performed using 2-teta scans at fixed fi and ki angles which were
varied by the 10 deg. step in a range of 0 – 90 deg. A drastic change of intensity of 202
peak in martensitic phase and sharp changes in mutual intensities of 220 and 400 peaks
in austenic phase as a function of ki was found while fi dependence was neglectful. An
analysis of the results leads to the conclusion about different degree of 110-type fiber
texture for the films of different thickness in both austenite and martensite states.
The perpendicular magnetic anisotropy as a result of fiber texturing and particular
microstructure of martensitic phase formed is proved experimentally for all the films.