Berlin 2008 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 23: Poster session

MM 23.44: Poster

Tuesday, February 26, 2008, 14:45–18:00, Poster B

Phase diagrams for the evolution of polydomain and polyvariant states in tetragonal ferromagnetic martensites — •Aristide T. Onisan¹, Nikolay S. Kiselev^1,2, Ulrich K. Rößler¹, and Alexei N. Bogdanov^1,2 — ¹IFW Dresden — ²Donetsk Institute for Physics and Technology

A continuum model for equilibrium microstructures in ferromagnetic twinned martensites is developed [1] that couples micromagnetic domain theory with anisotropic crystal elasticity and is applicable for magnetic shape memory materials as the Ni-Mn-Ga Heusler alloys. The approach considers the twin variant redistribution in tetragonal martensites with no-slip condition at the twin boundaries, magnetic 180^∘-domain structures within twins, and the rotation of magnetization within domains due to finite magnetic anisotropies. For two-variant twinned single crystals, we calculate equilibrium phase diagrams, strain and magnetization curves under combined external magnetic fields and stresses within the thermodynamic phase theory approximation. The limitations of the phase-theory approximation are discussed. For three-variant twinned microstructures, we show that magnetic charges arise internally at the twin boundaries. [1] A.N. Bogdanov, A. DeSimone, S. Müller, U.K. Rößler, J. Magn. Magn. Mater. 261 (2003) 204. Supported by DFG, SPP 1239 project A08.