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MA: Fachverband Magnetismus

MA 51: Magnetic Shape Memory Alloys (Joint Session with MM)

MA 51.11: Vortrag

Freitag, 20. März 2015, 12:00–12:15, H 0112

Density functional and tight-binding analysis of energy balance between L1₀ and L2₁ structures in Ni-Mn-X (X=Ga, Sn, In) Heusler alloys — •Ingo Opahle, Georg K. H. Madsen, and Ralf Drautz — ICAMS, Ruhr-Universität Bochum, Germany

The energy balance between the cubic L2₁ austenite structure and the tetragonal L1₀ martensite structure of Ni-Mn-X (X=Ga, Sn, In) Heusler alloys is analyzed using density functional theory and tight-binding (TB) models. Without spin-polarization the L1₀ structure with c/a>1 is favoured over the cubic L2₁ structure. In contrast, magnetic contributions are found to stabilize the cubic austenite structure. The presence or absence of a martensitic ground state is determined by a subtle energy balance between the magnetic contributions and the nonmagnetic energy gain by a tetragonal distortion. The role of the electron per atom (e/a)-ratio, the size of the p-element X and the Jahn-Teller distortion for the martensitic transition temperature in the Ni-Mn-X Heusler alloys is discussed. The absence of a martensitic ground state in stoichiometric Ni₂MnIn can be understood from the different contributions of the p-element to the bond energy in the TB model compared to Ni₂MnGa.