Regensburg 2004 – wissenschaftliches Programm
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MA: Magnetismus
MA 24: Symposium Magnetic Shape Memory Alloys (zusammen mit M)
MA 24.5: Vortrag
Donnerstag, 11. März 2004, 12:45–13:00, H23
Modulated martensitic structures in MBE-grown NiMnAl magnetic shape memory alloys — •Sigurd Thienhaus1, Ralf Hassdorf1, Jürgen Feydt1, Rene Borowski1, Markus Boese2, and Michael Moske1 — 1Forschungszentrum caesar, 53175 Bonn — 2Universität Bonn, Institut für Anorganische Chemie, 53117 Bonn
Composition spreads close to the Heusler alloy Ni2MnAl were grown onto four-inch wafer substrates by molecular beam epitaxy. Compositional variations of around 10 at.% relative to each constituent enable a direct comparison of the chemical-structural relationship with respect to martensitic transformation and to magnetic ordering as well as an efficient identification of the emerging phase stability regions. In our study, we set the primary focus on the structural aspects of the transformation behavior as confirmed by X-ray microdiffraction in combination with a specially designed heating stage. Notably, high-resolution cross-sectional TEM imaging of the respective composition areas reveals a laminated two-phase martensitic structure within the single grains, identified as a sequence of 2M and 14M variants. Stress relief upon transformation is observed during thermal processing in a bending-beam stress apparatus and ranges from 50 to 200 MPa depending on the composition. Vibrating-sample magnetometry so far suggests magnetic ordering to occur well below room temperature. In this context, the compositional and microstructural aspects of the phase stabilities will be discussed.