Project Details
Projekt
Basic research of the influence of real structure on the magnetic field induced strain in NiMnGa alloys - Structure and properties of twin boundaries in NiMnGa alloys
Applicant
Professor Dr. Werner Skrotzki
Subject Area
Materials Science
Term
from 2006 to 2013
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 28300371
The magnetic field induced strain (MFIS) is based on the comparably easy motion of twin boundaries under magnetic fields, and a high magnetic anisotropy. To develop new MFIS materials, respectively optimize the MFIS effect of known materials, it is a challenge to understand the physical processes determining the motion of twin boundaries in these materials. Twin boundary motion, like grain boundary motion in general, is affected by parameters such as order, deviation from stoichiometry, modulation, precipitates, grain size, texture and domain structure. Therefore, it is the task of the project to systematically investigate the effect of these parameters on the MFIS effect in NiMnGa alloys. These alloys are chosen, because they are showing the biggest MFIS so far, and casting can quite easily produce materials in bulk form. The investigations planned comprise a detailed characterization of the structure of the twin boundary as well as of the crystallographic and magnetic microstructural features mentioned above. Characterization will be done at highest standards by means of conventional transmission electron microscopy (TEM), Lorentz electron microscopy, and electron holography, both at medium and high resolution. Basic research on these issues will comprehensively be performed using single crystals. Since for the intended application of MFIS in technology, e.g. for actuators and sensors, polycrystalline materials seem to be more appropriate, the specific polycrystalline aspects have to be considered: The modifications of the MFIS effect by grain size and texture will be analyzed. Furthermore their influence on twin boundary motion will be studied by mechanical tests in a large temperature range, also with simultaneously applying a magnetic field.
DFG Programme
Priority Programmes
