Usual real samples of ferromagnetic shape memory alloys contain complex systems of crystallographic and magnetic domains [1,2]. We apply a phenomenological theory [3] to describe the evolution of multidomain states driven by external magnetic field and external stresses in magnetic shape-memory materials. Magnetization processes under external stress and magnetic fields can be analysed based on phase diagrams from phase-theory approximation that is applicable for volume systems. Generalizations allow (i) to introduce 180-degree magnetic domain structures within the twin variants and (ii) rotation of magnetic moments within magnetic domains in case of relatively weak magnetic anisotropies. Hysteretic processes can be described by an effective relaxation equation, which accounts for a thermally activated twin boundary motion. Geometrical domain models with 90-degree magnetization stripe structure allow to derive characteristic lengths of thermodynamically stable coupled multidomain structures applicable to twinned platelets or thin films with two homogeneously magnetized variants. The application of the theory for (textured) polycrystalline materials through an effective (mean-field) coupling in an assembly of variously oriented single-crystals is demonstrated. [1] O. Söderberg et al. Smart Mater. & Struct. 14 (2005) S223. [2] V. A. Chernenko et al. J. Phys.: Condens. Matter 17 (2005) 5215, Acta Mat. 53 (2006) 5461. [3] A. N. Bogdanov, A. DeSimone, S. Müller, U. K. Rößler, J. Magn. Magn. Mater. 261 (2003) 204.

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1. Magnetic structures and magnetization processes in layered systems with antiferromagnetic couplings
2. Magnetoresistance and magnetization processes in the helimagnetic compound DyMn₆Ge₆ and in related alloys Dy(Mn₆Ge₆)_1-x(Fe₆Al₆)_x