Advanced Study Group Ab Initio Based Modelling (ABM)
Designing shape-memory Heusler alloys from first-principles
M. Siewert, M. Gruner, A. Dannenberg, A. Chakrabarti, H. Herper, M. Wuttig, S. Barman, S. Singh, A. Al-Zubi, T. Hickel, J. Neugebauer, M. Gillessen, R. Dronskowski, P. Entel.
Applied Physics Letters, 99, 191904, (2011)
The phase diagrams of magnetic shape-memory Heusler alloys, in particular, ternary Ni-Mn-Z and quarternary (Pt, Ni)-Mn-Z alloys with Z = Ga, Sn, have been addressed by density functional theory and Monte Carlo simulations. Finite temperature free energy calculations show that the phonon contribution stabilizes the high-temperature austenite structure while at low temperatures magnetism and the band Jahn-Teller effect favor the modulated monoclinic 14M or the nonmodulated tetragonal structure. The substitution of Ni by Pt leads to a series of magnetic shape-memory alloys with very similar properties to Ni-Mn-Ga but with a maximal eigenstrain of 14%.
Keyword(s): density functional theory; free energy; gallium alloys; Jahn-Teller effect; manganese alloys; Monte Carlo methods; nickel alloys; phase diagrams; platinum alloys; shape memory effects; tin alloys