Role of shuffles and atomic disorder in Ni-Mn-Ga

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:378

Article; Proceedings Paper

Zayak, AT ; Entel, P

关键词: Ni2MnGa;    martensitic phase;    modulation;    tetrahedral distortions;   

DOI  :  10.1016/j.msea.2003.10.368

来源: Elsevier

【 摘 要 】

We report results of ab initio calculations of the ferromagnetic Heusler alloy Ni2MnGa. Particular emphasis is placed on the stability of the low temperature tetragonal structure with c/a = 0.94. This structure cannot be derived from the parent L2(1) structure by a simple homogeneous strain associated with the soft elastic constant C. In order to stabilize the tetragonal phase, one has to take into account shuffles of atoms, which form a wave-like pattern of atomic displacements with a well defined period (modulation). While the modulation is related to the soft acoustic [110]-TA(2) phonon mode observed in Ni2MnGa, we obtain additional atomic shuffles, which are related to acoustic-optical coupling of the phonons in Ni2MnGa. In addition, we have simulated an off-stoichiometric system, in which 25% of Mn atoms are replaced by Ni. The energy of this structure also exhibits a local minimum at c/a = 0.94. This allows us to conclude that both shuffles and atomic disorder stabilize the c/a = 0.94 structure. In both cases the stability seems to be associated with a dip in the minority-spin density of states (DOS) at the Fermi level, being related to the formation of hybrid states of Ni d and Ga p minority-spin orbitals. (C) 2004 Published by Elsevier B.V.

【 授权许可】

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