Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 17: Magnetic Shape Memory Alloys

MA 17.6: Talk

Wednesday, March 28, 2007, 16:30–16:45, H10

Structural and mechanical properties of NiMnGa shape memory ferromagnets — •Uwe Gaitzsch¹, Stefan Roth¹, Andrea Böhm², Bernd Rellinghaus¹, and Ludwig Schultz¹ — ¹IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany — ²Fraunhofer IWU, Nöthnitzer Str. 44, D-01187 Dresden, Germany

Magnetic shape memory alloys are of significant research interest owing to their capability to deform quasi-plastically by some percent via twin boundary motion under the influence of a magnetic field. These materials are supposed to react faster than conventional shape memory materials because neither heating nor cooling are involved. We present the structural and mechanical properties of polycrystalline, textured Ni₅₀Mn₃₀Ga₂₀ and Ni₅₀Mn₂₉Ga₂₁. Upon cooling, these alloys undergo austenite-martensite transitions at 100^oC and 55^oC, respectively. The evolving martensitic structure is either orthorhombic or tetragonal and depends on the thermomechanical history of the samples and their composition. Since only two of the three possible martensitic structures are capable of providing the mandatory highly moblile twin boundaries, it is essential to understand and control the phase formation process by appropriate thermal and mechanical treatment. Once the sample is given a suitable structure, samples for magnetomechanical testing are hot mold cast for directional solidification and investigated in magnetic fields of up to 0.8 T in compression tests.