Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 13: Poster Ia: Electron Theory (1); Magnetic Imaging (2,3); Thin Films (4-25); MSMA (26-33); Magn. Semiconductors (34-42); Magn. Half Metals and Oxides (43-60)

MA 13.29: Poster

Dienstag, 24. März 2009, 10:15–13:00, P1A

In-situ studies of the martensitic transformation in epitaxial Ni-Mn-Ga films — •Robert Niemann^{1, 2}, Jörg Buschbeck¹, Oleg Heczko^{1, 3}, Michael Thomas¹, Ludwig Schultz^{1, 2}, and Sebastian Fähler^{1, 2} — ¹IFW Dresden, P.O. Box: 270116, 01171 Dresden, Germany — ²Institute for Solid State Physics, Department of Physics, Dresden University of Technology, 01062 Dresden, Germany — ³Institute of Physics, Academy of Science of Czech Republic, Na Slovance 2, 18205 Prague, Czech Republic

The martensitic transformation of epitaxial Ni-Mn-Ga films on rigid substrates is examined with respect to changes of structure, microstructure, magnetic and electronic properties. For this, temperature dependent atomic force microscopy (AFM), X-ray, magnetization and resistivity measurements are used. The combination of these in-situ methods give a comprehensive understanding of the martensitic transformation and allows to identify differences of constrained epitaxial films compared to bulk. Experiments show the formation of a twinned, orthorhombic martensite with high uniaxial magnetocrystalline anisotropy from the austenite around room temperature. While most features are similar to a first order transformation, the transformation proceeds continuously to lower temperatures, an effect which could be explained by the constrain of the rigid substrate. The high-resolution AFM micrographs directly reveal how martensite variants grow and show the converging of variants from different nucleation origins. A crystallographic modell is presented which explains the regular, triangular morphology observed by AFM in the martensite state.