Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 29: Magnetische Materialien

MA 29.7: Vortrag

Dienstag, 8. März 2005, 16:45–17:00, TU A060

Adjusting the crystal structure of NiMnGa ferromagnetic shape memory alloys — •Uwe Gaitzsch, Stefan Roth, Norbert Mattern, Bernd Rellinghaus, and Ludwig Schultz — IFW Dresden, Helmholtzstr. 20, 01069 Dresden

The intermetallic phase Ni₂MnGa is known to exhibit large magnetic field induced strain (MFIS) due to magnetically driven rearrangements of martensitic variants within a wide compositional range. Samples of Ni_100−x−yMn_xGa_y with (x,y) = (26,22) and (x,y) = (30,20) were prepared by arc or induction melting of the elements in Argon. Se (0,1%) was added to one of the samples to investigate phase stabilizing effects. Annealing at and below the ordering temperature (B2-L2₁ type, roughly 750^oC) followed by water quenching was found to have an influence on the structure of the martensitic phase, which forms between 50^oC and 100^oC as determined by DSC. X-ray diffraction was used to characterize the structure: In ball milled powder samples, the structure was found to be tetragonal for (x,y) = (26,22) and orthorhombic with some monoclinic distortion for (x,y) = (30,20) thereby indicating the seven-layered (7M) type of martensite. The magnetic anisotropy field was measured using the singular point detection technique. Compression tests up to 150 MPa resulted in persistent deformations. Whereas it was possible to recover the original shape by thermal treatments, magnetically induced recovery was not achieved in fields up to 2 T.