Magnetic, magnetoelastic and dynamical properties of martensitic Heusler alloys

• Applicant: Professor Dr. Mehmet Acet
• Subject Area: Materials Science
• Term: from 2006 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 28320387

The discovery of the effect of large magnetic field induced strains (~10 %) in the martensiticstate of Ni-Mn-Ga has promoted interest not only relevant to technological applications, butalso to research devoted to the understanding of the basic mechanisms underlying the cause ofthese strains. This type of field induced strain is known as the magnetic shape memory effectand is caused by the reorientation of martensite variants by twin boundary motion. Results ofelectronic structure calculations and the observation of the systematic variation of themartensitic transformation temperatures with valence electron concentration suggest theoccurrence of martensitic transformations in various Heusler systems other than Ni-Mn-Ga.We have recently observed such transformations in polycrystalline Ni-Mn-In and Ni-Mn-Sn,where in particular, Ni-Mn-In exhibits a field induced strain of size similar to that forpolycrystalline Ni-Mn-Ga. In the course of the present project, we aim to introduce newmagnetic Heusler materials exhibiting large magnetic field induced strains. We use asystematic approach based on employing results of phonon spectrum calculations and data onthe valence electron concentration dependence of the martensitic transformation temperatureto find potential magnetic shape memory materials and investigate their magnetic and elasticproperties. Work will be carried out on both polycrystalline and single crystal material. Thesearch for new Heusler material exhibiting martensitic transformations will be carried outwith polycrystalline material using temperature and magnetic field dependent magnetizationand strain studies. Materials which show magnetic field induced structural modificationeffects at particular compositions will be prepared in single crystal form with singlemartensite variants to investigate the lattice dynamics and structural properties using neutronscattering and diffraction techniques in magnetic fields. These will be done in collaborationwith our consortium partners. We will also examine field induced strains and magneticproperties on single variant samples to exploit the systems for their maximum availablestrains.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1239: Modification of Microstructure and Shape of Solid Materials by External Magnetic Fields
• Participating Person: Professor Dr. Eberhard F. Wassermann (†)