Berlin 2008 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 36: Phase Transitions II
MM 36.1: Vortrag
Donnerstag, 28. Februar 2008, 11:45–12:00, H 0107
First Principles Investigation of Twin Boundary Motion in Magnetic Shape Memory Heusler Alloys — •Markus Ernst Gruner and Peter Entel — Fachbereich Physik, Universität Duisburg-Essen, 47048 Duisburg, Germany
In the martensitic phase of the magnetic shape memory (MSM) Heusler alloy Ni2MnGa, strains of up to 10 % can be induced by external magnetic fields, making the material a technologically relevant candidate for magneto-mechanical actuators. The MSM effect in near stoichiometric Ni2MnGa is connected with a modulated pseudotetragonal martensitic phase with c/a<1. It is attributed to a high mobility of
the twin-boundaries in connection with a large magneto-crystalline anisotropy allowing the reorientation of martensitic twins with the help of a magnetic field thereby changing the shape of the crystal.
So far, the origin of the high mobility of twin-boundaries in this phase is unresolved and empirical potentials
permitting the simulation on the relevant length and time scales do not exist. We therefore attempt to close this gap by large scale ab initio calculations in the framework of density functional theory allowing the investigation of simplified models of martensitic twin boundaries for the different martensitic
structures of Ni2MnGa with the help of contemporary supercomputers. First results indicate that for the low-temperature, non-modulated martensitic L10 structure with c/a>1, the energy needed for shifting a twin boundary
is too large to be overcome by magneto-crystalline anisotropy.
[1] M. E. Gruner, P. Entel, I. Opahle, M. Richter, J. Mater. Sci. (accepted for publication)