Regensburg 2019 – scientific programme

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MA: Fachverband Magnetismus

MA 15: Magnetism Poster A

MA 15.60: Poster

Tuesday, April 2, 2019, 10:00–13:00, Poster E

3D check board pattern formation of martensite/austenite domains in NiCoMnAl shape memory alloys — •Andreas Becker, Daniela Ramermann, Martin Gottschalk, Inga Ennen, Björn Büker, Tristan Matalla-Wagner, Andreas Hütten, and Günter Reiss — Center for Spinelectronic Materials and Devices, Physics Department, Bielefeld University, 33615 Bielefeld, Germany

NiMnX (X=Al,Ga,Sn,In) magnetic shape memory Heusler alloys are considered as promising materials for magnetocaloric cooling applications due to their magnetoelastic coupling near room temperature. However most of them show a very large thermal hysteresis, which limits their potential in future applications.

Thin martensite interclations in thin films could be benificial for transforming films, because the formation energy during martensite nucleation is reduced. Our aim is to decrease the thermal hysteresis in off-stoichiometric NiCoMnAl thin films by preparing multilayer systems, which consist of alternatively grown martensite intercalations and active transforming austenitic layers. The stoichiometry of these two layers is chosen in such a way that their thermal hysteresis do not overlap.

Temperature dependent magnetization measurements show a significant decrease in hysteresis width as a function of the number of martensite intercalations. If the austenite active layers have a similar thickness compared to the martensite intercalations a 3D check board pattern becomes visible in HRTEM cross section images. The contrast is due to alternating martensite/austenite domains.