Regensburg 2010 – scientific programme

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MA: Fachverband Magnetismus

MA 8: Magnetic Shape Memory Alloys

MA 8.10: Talk

Monday, March 22, 2010, 17:45–18:00, H22

High resolution imaging of epitaxial Ni-Mn-Ga films with STM — •Philipp Leicht¹, Aleksej Laptev¹, Mikhail Fonin¹, Yuansu Luo², and Konrad Samwer² — ¹Fachbereich Physik, Universität Konstanz — ²I. Physikalisches Institut, Universität Göttingen

Magnetic shape memory (MSM) alloys are of great interest due to their possible application as actuators or sensors. Upon cooling from the high temperature austenite phase a structural phase transformation to a distorted martensite phase occurs. MSM films deposited on substrates accommodate the strain associated with the martensite transition by formation of twin boundaries [1]. Here epitaxial off-stoichiometric Ni-Mn-Ga films were grown on MgO substrates by dc-magnetron sputtering. The surface of the films was investigated in ultra high vacuum conditions by means of scanning tunneling microscopy (STM) at room temperature. Austenitic areas reveal atomically flat terraces separated by steps with an average height corresponding to the distance between equivalent atomic planes of the bulk L2₁ structure. STM images on martensitic areas reveal a wavy-like structure due to the formation of twin boundaries. An additional superstructure on every second variant in form of narrow stripes running perpendicular to the twin boundaries was observed. The latter structure is explained on the basis of a structural model taking into account the twinning and the shuffling of atomic planes in layered martensites (5M, 7M) [2]. This work is supported by BMBF-projects MSM-Sens 13N10061 and 13N10062.

[1] J. Buschbeck et al., Acta Materialia 57, 2516-2526 (2009)

[2] V. V. Martynov et al., J. Phys. III France 2, 739-749 (1992)