Ab initio investigation of twin boundary motion in the magnetic shape memory Heusler alloy Ni2MnGa
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Magnetic shape memory (MSM) alloys, which transform martensitically below the Curie temperature in the ferromagnetic (FM) state, represent a new class of actuators. In Ni2MnGa, unusually large magnetic field-induced strains of about 10% have been observed. This effect is related to a high mobility of martensitic twin boundaries in connection with a large magneto-crystalline anisotropy. MSM materials exist in a variety of different martensitic structures depending on temperature and compositions. We investigate the energetics of L10 phase twin boundary motion quasi-statically with ab initio methods and relate the results to calculations of the magneto-crystalline anisotropy energy. Our results indicate that for the L10 structure the energy needed for a coherent shift of a twin boundary may be too large to be overcome solely by magnetic field-induced strains.
KeywordsTwin Boundary Martensitic Variant Orbital Moment Local Spin Density Approximation Hard Axis
We would like to thank U. K. Rößler for helpful discussions and a careful proofreading of the manuscript. Large parts of the calculations were performed on the IBM Blue Gene/L supercomputer of the John von Neumann Institute for Computing at Forschungszentrum Jülich, Germany. We thank the local staff for their support and Dr Pascal Vezolle of IBM for his efforts in optimizing the VASP binary for the Blue Gene/L architecture. The atomistic visualizations in Fig. 5 were prepared using XCrySDen . Financial support was granted by the Deutsche Forschungsgemeinschaft through the Priority Programme SPP1239, Change of microstructure and shape of solid materials by external magnetic fields.
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