Magnetic, magnetoelastic and dynamical properties of martensitic Heusler alloys - Ab initio and semi-empiric simulations of structural changes of magnetic shape memory systems by external magnetic fields

用第一性原理计算方法研究了Heusler化合物X_2YZ（X = Fe，Co，Ni，Cu; Y = Mn，Fe，Co; Z = Al，Ga，Ge，In，Sn）的高对称性立方结构的结构不稳定性.价电子与原子比e/a的作用的初步调查表明，原子间力常数的系统趋势，这是一个指标的结构（马氏体）不稳定性。在本项目中，我们将通过计算结构、电子、磁性和电子-声子性质来继续这些从头算研究，主要集中在新的磁性形状记忆系统Ni-Mn-In，Ni-Mn-Sn、Ni-Mn-Sb和Ni-Mn-（Ga-In）。最近对Ni 2 MnIn的研究表明，在原子水平上，外磁场对微观结构的影响可以用固定自旋矩方法在从头计算中很好地考虑。

First-principles calcutations have been used to investigate chemical trends in the structural instability of the high-symmetry cubic structure for a selected set of Heusler compounds X2YZ (X = Fe, Co, Ni, Cu; Y = Mn, Fe Co; Z = Al, Ga, Ge, In, Sn). Preliminary investigations of the role of the valence-electron-to-atom ratio e/a have shown systematic trends in the interatomic force constant, which is found to be an indicator of the structural (martensitic) instability.In this project, we will continue these ab initio investigations by calculating the structural, electronic, magnetic and electron-phonon properties, mainly concentrating on the new magnetic shape memory systems Ni-Mn-In, Ni-Mn-Sn, Ni-Mn-Sb and Ni-Mn-(Ga-In). A recent study of Ni2MnIn has shown that the effect of an external magnetic field on the microstructure at an atomic level can well be taken care of in the ab initio calculations by using the fixed-spin moment method.