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 13.31: Poster

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

Domain models for ferromagnetic shape-memory alloys:
magnetic phase diagrams, transformation and magnetization processes — •Aristide T. Onisan, Alexei N. Bogdanov, and Ulrich K. Rößler — IFW Dresden, POB 270116, 01171 Dresden

A phenomenological domain theory for magnetic shape memory materials is developed for the case of a ferromagnetic martensite with tetragonal twin variants, as a simplified approach to the archetypical Ni₂MnGa Heusler alloys. A three dimensional model is analysed that is derived from a micromagnetic continuum approach combined with piecewise linear crystal elasticity of the twin variants. The tetragonal variants are assumed to own easy-axis magnetic anisotropy. The phase theory approximation is used to treat the equilibrium domain structure which is composed of six phases describing the two magnetic domains within each of the three possible twin variants created in an austenitic cubic single crystal. Phase diagrams under magnetic fields and stresses have been calculated in the three-dimensional case for a macroscopic sample with ellipsoidal shape. We have also calculated switching fields and the theoretical maximum hysteresis for two-dimensional geometries where only two twin-variants are present and twin-rearrangement is impeded by coercivity. Our results for realistic materials parameters are compared with existing experimental data.