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KR: Fachverband Kristallographie

KR 10: Poster: Multiferroics (with MA, DF, KR, DS)

KR 10.61: Poster

Dienstag, 23. März 2010, 10:45–13:45, Poster A

Surface structure and electronic properties of epitaxial off-stoichiometric Ni-Mn-Ga films — •Aleksej Laptev¹, Philipp Leicht¹, Mikhail Fonin¹, Yuansu Luo², Konrad Samwer², Yuriy Dedkov³, and Martin Weser³ — ¹Fachbereich Physik, Universität Konstanz, 78457 Konstanz — ²I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen — ³Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin

Ni₂MnGa alloys have attracted considerable interest due to the large magnetic field-induced strain and their possible applications as microscale actuators or sensors. Upon cooling from the austenite phase a transformation to the martensite phase occurs for these materials. Here we report on the investigation of epitaxial off-stoichiometric Ni-Mn-Ga films grown on MgO substrates by dc-magnetron sputtering. To achieve appropriate surface quality the samples were treated under ultra high vacuum conditions by repeated cycles of sputtering and annealing. The crystal structure changes at the Ni-Mn-Ga (100) surface during the reversible phase transition were followed by LEED. A splitting of the main reflexes due to a longer range ordering of the surface was observed upon cooling. The twin boundary formation together with the modulation of the structure was imaged by high resolution STM in the martensite phase. Electronic properties were investigated by ultra-violet photoemission spectroscopy showing pronounced differences in the valence band spectra of two phases. Financial support by the BMBF within MSM-Sens 13N10061 and 13N10062 is gratefully acknowledged.