Regensburg 2007 – scientific programme
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MA: Fachverband Magnetismus
MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)
MA 15.154: Poster
Tuesday, March 27, 2007, 15:00–19:00, Poster A
Phenomenological models for magnetic shape memory materials — •Ulrich K. Rößler1, Nicloai S. Kiselev2, Igor E. Dragunov1,2, and Alexei N. Bogdanov1,2 — 1IFW Dresden — 2Donetsk Institute for Physics and Technology
A phenomenological theory for magnetic shape-memory effects [1] for twinned ferromagnetic martensites with tetragonal lattice structure is described and extended. The theory couples micromagnetic continuum theory for magnetization distribution and linear elasticity in the twin variants. Magnetization processes under external stress and magnetic fields can be analysed based on phase diagrams from the 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] U. K. Rößler, A. N. Bogdanov, A. DeSimone, S. Müller, U. K. Rößler, J. Magn. Magn. Mater. (2002).